| 1. |
- Crocetti, Roberto, et al.
(författare)
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An Innovative Prefabricated Timber-Concrete Composite System
- 2014
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Ingår i: Materials and Joints in Timber Structures. - Dordrecht : Springer Netherlands. - 2211-0844 .- 2211-0852. - 9789400778108 ; 9, s. 507-516
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Konferensbidrag (refereegranskat)abstract
- A novel type of timber-concrete composite floor, consisting of longitudinal glulam beams with a fibre reinforced concrete (FRC) slab on the top is proposed. In order to check some relevant mechanical properties of such a floor, full-scale laboratory tests along with numerical analyses were carried out. The shear connector system used in the investigation consisted of self-tapping screws driven at an angle of 45 degrees to the grain direction of the glulam beams. The manufacture of the structure occurred according to the following steps: (a) the screws were inserted on the top of the glulam beams; (b) the beams were rotated 180 degrees about the longitudinal axis and placed in a concrete formwork; (c) the FRC was cast into the formwork; (d) after curing of the FRC, the composite floor was again rotated 180 degrees about the longitudinal axis into its right position, i.e. with the FRC slab on the top side. Long term tests and quasi-static bending tests were performed. It was found that the proposed connection system showed a very high degree of composite action both during the long-term testing and at load levels close to the failure load. Furthermore, the assembly of the prefabricated timber-concrete composite system revealed to be very fast and easy.
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| 2. |
- Abrahamsen, Rune, et al.
(författare)
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Dynamic Response of Tall Timber Buildings Under Service Load : The DynaTTB Research Program
- 2020
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Ingår i: EURODYN 2020, XI international conferece on structural dynamics. - : National Technical University of Athens. - 9786188507210 ; , s. 4900-4910
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Konferensbidrag (refereegranskat)abstract
- Wind-induced dynamic excitation is becoming a governing design action determin-ing size and shape of modern Tall Timber Buildings (TTBs). The wind actions generate dynamic loading, causing discomfort or annoyance for occupants due to the perceived horizontal sway – i.e. vibration serviceability failure. Although some TTBs have been instrumented and meas-ured to estimate their key dynamic properties (natural frequencies and damping), no systematic evaluation of dynamic performance pertinent to wind loading has been performed for the new and evolving construction technology used in TTBs. The DynaTTB project, funded by the Forest Value research program, mixes on site measurements on existing buildings excited by heavy shakers, for identification of the structural system, with laboratory identification of building elements mechanical features coupled with numerical modelling of timber structures. The goal is to identify and quantify the causes of vibration energy dissipation in modern TTBs and pro-vide key elements to FE modelers.The first building, from a list of 8, was modelled and tested at full scale in December 2019. Some results are presented in this paper. Four other buildings will be modelled and tested in spring 2020.
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| 3. |
- Abrahamsen, Rune, et al.
(författare)
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Dynamic response of tall timber buildings under service load : results from the dynattb research program
- 2023
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Ingår i: World Conference on Timber Engineering 2023 (WCTE 2023). - : Curran Associates, Inc.. - 9781713873297 ; , s. 2907-2914
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Konferensbidrag (refereegranskat)abstract
- Wind-induced dynamic excitation is a governing design action determining size and shape of modern Tall Timber Buildings (TTBs). The wind actions generate dynamic loading, causing discomfort or annoyance for occupants due to the perceived horizontal sway, i.e. vibration serviceability problem. Although some TTBs have been instrumented and measured to estimate their key dynamic properties (eigenfrequencies, mode shapes and damping), no systematic evaluation of dynamic performance pertinent to wind loading had been performed for the new and evolving construction technologies used in TTBs. The DynaTTB project, funded by the ForestValue research program, mixed on site measurements on existing buildings excited by mass inertia shakers (forced vibration) and/or the wind loads (ambient vibration), for identification of the structural system, with laboratory identification of building elements mechanical features, coupled with numerical modelling of timber structures. The goal is to identify and quantify the causes of vibration energy dissipation in modern TTBs and provide key elements to finite element models. This paper presents an overview of the results of the project and the proposed Guidelines for design of TTBs in relation to their dynamic properties.
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| 4. |
- Al-Emrani, Mohammad, 1967, et al.
(författare)
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Strengthening Glulam Beams with Steel and Composite Plates
- 2009
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Ingår i: Proceedings of the 7th International Conference on Composite Science and Technology, Sharjah, UAE.
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Konferensbidrag (refereegranskat)abstract
- The stiffness requirements in the design of timber beams in serviceability limit state is a factor that often makes it necessary to increase the beam dimensions beyond what is required for strength. This causes increased material use and thus higher production costs. This study is an effort to investigate the viability of using Steel and CFRP (carbon fibre reinforced polymers) as reinforcement in new glulam beams. By gluing CFRP to the tension side of the beam it is possible to move the fracture from tensile rupture to the compression side of the beam which is beneficiary due to the more ductile behaviour of wood in compression. In the experimental part of the investigation, nine glulam beams strengthened with bonded steel and CFRP-laminates were tested to failure. The effect of various geometrical properties for the laminates was investigated, as well as strengthening with different amounts of laminates on the tension and compression side.
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| 5. |
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| 6. |
- Bergenudd, Jens, et al.
(författare)
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Dynamic analysis of a pedestrian timber truss bridge at three construction stages
- 2024
-
Ingår i: Structures. - : Elsevier BV. - 2352-0124. ; 59
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Tidskriftsartikel (refereegranskat)abstract
- This article investigates the dynamic behaviour of a single span pedestrian timber truss bridge by in situ testing and numerical modelling. The in situ dynamic tests were performed at three different construction stages: (1) on only the truss structure, (2) on the finished bridge without the asphalt layer and (3) on the finished bridge with the asphalt layer. The objective is to better understand how the different parts of the bridge contribute to the overall dynamic properties. The experimental results show that the damping ratios increased significantly for the first lateral mode (from 1.0 to 3.8%) and the first torsional mode (from 1.2 to 3.5%) between stage 2 and stage 3 due to the asphalt layer. The damping ratio is around 1.6% for the first bending mode for the finished bridge. The experimental and numerical results indicate that the stiffness of the asphalt layer is important to consider at stage 3 (10 degrees C) for the first lateral and torsional mode, but not for the first bending mode. Finally, it was concluded that longitudinal springs must be applied at the pot bearings in order to get agreement with the experimental results at all the three stages.
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| 7. |
- Bergenudd, Jens
(författare)
-
Dynamic properties of two pedestrian timber bridges : Experimental and numerical analysis at several stages of construction
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Pedestrian bridges can beneficially be made from timber in order for our society to reach a sustainable future. This positive development is partly made possible due to advances in engineered wood products (e.g. glued laminated timber) and the possibilities for pre-fabrication of structural parts. Timber bridges, especially long and slender, can however be susceptible to uncomfortable vibrations which could be solved by more accurate dynamic analysis in the design phase. Common issues reported by previous research are the difficulties in accurate predictions of the natural frequencies without calibration against experimental results. The purpose with the present research work is therefore to perform dynamic analysis of two pedestrian timber bridges at different construction stages in order to better understand the influence of different structural parts in the numerical models. The results show that the estimated and applied values for the densities of the timber (Norway spruce and Scots pine) are slightly higher than in the norm. Both bridges required calibration of longitudinal stiffness at the supports for the numerical results to agree with the experiments. The railings could be omitted from the numerical models for both bridges, which is in contrast with common engineering practise where they are often considered as an additional mass. The stiffness of the asphalt was required at low temperatures (10 °C and 0 °C). However, the asphalt could be modelled as an additional mass at a high temperature (40 °C) where special care also could be given to the effects of the composite cross-section geometry (timber deck and asphalt). The level of detail for the modelling of the truss joints, the connection truss/crossbeam and the connection deck/crossbeams proved to be an important issue for the Stela bridge. The damping ratios (ζ) increased with an asphalt layer on the bridge and are slightly higher than the values recommended by the norms. This may be relevant to consider in the design phase. However, it may be difficult to derive general conclusions for other pedestrian timber bridges since this thesis only concerns case studies of two bridges. More studies of other types of bridges are therefore necessary in order to confirm or disprove the present results
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| 8. |
- Bergenudd, Jens, et al.
(författare)
-
Dynamic testing and numerical modelling of a pedestrian timber bridge at different construction stages
- 2023
-
Ingår i: Engineering structures. - : Elsevier BV. - 0141-0296 .- 1873-7323. ; 279
-
Tidskriftsartikel (refereegranskat)abstract
- This article studies the dynamic properties of a single span pedestrian timber bridge by in-situ testing and numerical modelling. The in-situ dynamic tests are performed at four different construction stages: (1) on only the timber structure, (2) on the timber structure with the railings, (3) on the timber structure with railings and an asphalt layer during warm conditions and (4) same as stage 3 but during cold conditions. Finite element models for the four construction stages are thereafter implemented and calibrated against the experimental results. The purpose of the study is to better understand how the different parts of the bridge contribute to the overall dynamic properties. The finite element analysis at stage 1 shows that longitudinal springs must be introduced at the supports of the bridge to get accurate results. The experimental results at stage 2 show that the railings contributes to 10% of both the stiffness and mass of the bridge. A shell model of the railings is implemented and calibrated in order to fit with the experimental results. The resonance frequencies decrease with 10–20% at stage 3 compared to stage 2. At stage 3 it is sufficient to introduce the asphalt as an additional mass in the finite element model. For that, a shell layer with surface elements is the best approach. The resonance frequencies increase with 15–30% between warm (stage 3) and cold conditions (stage 4). The stiffness of the asphalt therefore needs to be considered at stage 4. The continuity of the asphalt layer could also increase the overall stiffness of the bridge. The damping ratios increase at all construction stages. They are around 2% at warm conditions and around 2.5% at cold conditions for the finished bridge.
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| 9. |
- Bergenudd, Jens, et al.
(författare)
-
Study of the dynamic response of a timber pedestrian bridge during different construction stages
- 2022
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Ingår i: Conference Proceedings 4th ICTB (2022) ,ICTB 2021 PLUS 4th International Conference on Timber Bridges. - Biel/Bienne, Switzerland. ; , s. 167-178
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The objective of this article is to study the dynamic behaviour of a timber pedestrian bridge by performing in-situ tests at four different construction stages: 1) on only the timber structure 2) on the timber structure with the railings 3) on the timber structure with railings and an asphalt layer during warm conditions and 4) same as stage 3 but during cold conditions. The study included numerical calculations with a 2D finite element model. Two modal parameter extraction methods were implemented during the post-processing. The modes of vibration were analysed with the modal assurance criterion (MAC) to ensure their validity. The results show that the presence of the railings during stage 2 increases the resonance frequencies with 0-2 % compared to stage 1, despite an approximately 5 % increase of the total mass of the bridge. The vertical resonance frequencies decreased 12-22 % when the asphalt was installed at stage 3 compared to stage 2, due to an approximately 70 % increase of the total mass and the asphalt’s low stiffness due to a high temperature. The resonance frequencies increased 14-27 % during cold conditions at stage 4 compared to stage 3. This was mainly due to an increased stiffness of the asphalt layer due to a low temperature. Adding railings therefore resulted in a higher overall stiffness of the bridge, whereas asphalt essentially only added mass to the bridge at warm conditions but increased the stiffness at cold compared to warm conditions. The damping ratios increased for each construction stage and were approximately 2-3 % for the finished bridge. The two modal parameter extraction methods produced similar results which ensures that reliable results are obtained. The auto-MAC indicated well-separated modes and the cross-MAC ensured comparison of the same modes. The finite element model showed that some stiffness was lacking for the first bending mode. This stiffness could be due to shear deformation of the plastic pads at the bridge supports.
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| 10. |
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| 11. |
- Blomqvist, Lars, 1962-, et al.
(författare)
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Development of novel structural connections - Inspiration from furniture industry
- 2021
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Ingår i: World Conference on Timber Engineering 2021, WCTE 2021. - Santiago, Chile : World Conference on Timber Engineering (WCTE).
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Konferensbidrag (refereegranskat)abstract
- The presented project aims to develop prototypes for building connections inspired by the furniture and interior industry and explore them with representatives from the timber construction industry. The long-term vision is that actors from furniture and building industry together develop a smart system for assembly of building elements, which provide higher precision, faster and more efficient assembly than what is available today. The prototype connection developed in this project shows that the idea is ripe for full-scale investigation. Laboratory tests showed promising results due to the high failure loads obtained with very high stiffness.
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| 12. |
- Blomqvist, Lars, 1962-, et al.
(författare)
-
EXPERIMENTAL AND NUMERICAL ANALYSES OF A CONNECTION FOR CLT STRUCTURES
- 2023
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Ingår i: Proceedings of the 2023 World Conference on Timber Engineering (WCTE). - Oslo, Norway : Curran Associates, Inc.. ; , s. 1154-1159
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Konferensbidrag (refereegranskat)abstract
- Although building systems made of cross-laminated timber (CLT) have become common in Sweden in the past 20 years and they have developed rapidly during the same period, steps remain to be taken to simplify the assembly of such systems, especially at construction sites. Current construction methods, however, remain labour-intensive and thus show room for improvement.This paper describes a novel connection for the assembly of building elements made of CLT. Simple and inexpensive, the connection is fairly insensitive to manufacturing tolerances and enables rapid, more efficient construction than the connections for CLT structures currently used. Test results show the excellent strength and stiffness of the connection, which also allows the replacement of numerous fasteners, including nails and screws, with only a single steel rod.
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| 13. |
- Crocetti, Roberto, 1968, et al.
(författare)
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Anchorage systems to reduce the loss of pre-stress in stress-laminated timber bridges
- 2010
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Ingår i: Proceeedings of the International Conference Timber Bridges. - 9788251926805 ; , s. 11-
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Konferensbidrag (refereegranskat)abstract
- Stress-laminated timber (SLT) decks consist of a number of planks, boards or glulam elements,placed edgewise, side by side, in which holes are pre-drilled at regular intervals along thelongitudinal axis. High-strength bars are then inserted into the holes and pre-tensioned. The pretensioningof the bars introduces compressive stresses in the transverse direction of the deck. Oneof the main problems with SLT decks has been the loss of tension in the pre-stressed bars, whichleads to a reduction in the structural efficiency of the deck. A phenomenon of this kind is mainlycaused either by local indentation of the wood at the anchorage system and/or by long-term effects.This paper describes the results of laboratory tests and numerical simulations conducted on SLTreinforced in the anchorage zones by means of self-tapping screws. The loss of tension in the prestressedbars has been recorded both instantaneously and after a few months in a climate chamberwhere they were exposed to moisture variation.
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| 14. |
- Crocetti, Roberto
(författare)
-
Bågar
- 2016. - 5
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Ingår i: Limträhandbok : Del 2. Projektering av limträkonstruktioner - Del 2. Projektering av limträkonstruktioner. - 9789198030464 ; , s. 153-165
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Bokkapitel (populärvet., debatt m.m.)
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| 15. |
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| 16. |
- Crocetti, Roberto, et al.
(författare)
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Experimental and numerical investigation on the shear strength of glulam
- 2010
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Ingår i: International Council for Research and Innovation in Building and Construction: Working Commission W18 ‑ Timber Structures — 2010. - Nelson : University of Canterbury.
-
Konferensbidrag (refereegranskat)abstract
- According to EC5, the shear resistance of a structural timber element should be determined on the basis of the characteristic shear strength of the material, along with classical beam theory. For glulam, the characteristic strength values are given by the European standard EN 1194 [3], which assumes a direct relationship between tensile strength and shear strength of the lamination. As an example, the characteristic shear strength of glulam class GL28c, consisting of inner laminations with characteristic tensile strength ft,0,k = 14.5 MPa, would be fv,k = 0.32·(14.5)^0.8 = 2.9 MPa. However, recent investigations both on glulam members [4] and on timber members [5] have shown that the shear strength of spruce is higher than the shear strength obtained by means of the model proposed by EN1194. Moreover, the studies show that the shear strength is nearly constant, regardless the strength class of the timber material.
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| 17. |
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| 18. |
- Crocetti, Roberto
(författare)
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Horisontell stabilisering
- 2016. - 5
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Ingår i: Limträhandbok : Del 2. Projektering av limträkonstruktioner - Del 2. Projektering av limträkonstruktioner. - 9789198030464 ; , s. 170-197
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Bokkapitel (populärvet., debatt m.m.)
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| 19. |
- Crocetti, Roberto, et al.
(författare)
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Innovative Timber-Concrete Composite Structures with Prefabricated FRC Slabs
- 2015
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Ingår i: Journal of Structural Engineering. - 0733-9445. ; 141:9
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Tidskriftsartikel (refereegranskat)abstract
- This paper concerns the development of innovative composite floor systems, comprising timber beams and prefabricated concrete slabs. For the development of this new system, two properties were regarded as vital, as follows: (1) good stiffness, and (2) a high degree of prefabrication. Shear connection systems installed using completely dry processes were used. Innovative and very efficient materials, such as fiber-reinforced concrete (FRC) and modified wood, were used for the manufacture of the specimens. The research reported in this paper was conducted in two phases, as follows: (1) the mechanical properties of different shear connectors were investigated (Phase A), and (2) on the basis of these experiment's results a second investigation was carried out in order to study the behavior of full-scale timber-concrete composite slabs (Phase B). During Phase A four different configurations, with a total of eight specimens, were laboratory tested in shear. During Phase B two full-scale floor elements, each with a different shear connection system, were laboratory tested in bending. The two shear connector systems used in the investigation were (1) shear anchor-keys of furfurylated wood, and (2) inclined steel tubes. Both of the proposed connection systems performed more than satisfactorily, showing a very high degree of composite action even at load levels close to the failure load. Moreover, it appeared that the assembling of the prefabricated fiber-reinforced concrete slab with the underlying beams occurred in an extremely easy manner. (C) 2014 American Society of Civil Engineers.
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| 20. |
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| 21. |
- Crocetti, Roberto, et al.
(författare)
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Multiple shear plane connections with timber based gusset plates
- 2021
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Ingår i: World Conference on Timber Engineering 2021, WCTE 2021. - : World Conference on Timber Engineering (WCTE).
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Konferensbidrag (refereegranskat)abstract
- This paper presents the results of an experimental study conducted on multiple-shear joints consisting of gusset plates made of either LVL or plywood connected to the timber members by means of full-threaded self-tapping screw. Both hardwood and softwood timber based gusset plates with different thickness and face grain orientations were investigated. The results show that this type of connection has an excellent structural performance, with not very dissimilar strength from that of comparable connections which makes use of slotted-in steel plates and dowels. It is believed, therefore, that the proposed solution can be a valid alternative to the more traditional timber connection with slotted-in steel plates and dowels.
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| 22. |
- Crocetti, Roberto, 1968
(författare)
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On some Fatigue Problems Related to Steel Bridges
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns three specific fatigue topics related to steel members in bridges, namely: (1) Modular Bridge Expansion Joints (MBEJs). Several premature fatigue failures of MBEJs have occurred in Europe and USA during the past decades. The principal cause of such failures has been an insufficient knowledge of the magnitude of the acting forces including dynamic effects. This has led to an inadequate design with respect to fatigue. In this thesis, a proposal for vertical and horizontal design loads acting on MBEJs is obtained by evaluating a large amount of field test data put at the author's disposal during his visit at Lehigh University, USA. A relatively simple model to describe the dynamic behaviour of MBEJs is also proposed. Reasonable load ranges based on traffic considerations as well as an adequate fatigue detail category based on laboratory tests is proposed for fatigue analysis of MBEJs. (2) Constant Amplitude Fatigue Limit (CAFL) for Riveted Connections. For old riveted steel bridge members an adequate estimate of the CAFL, i.e. the stress range level below which there will be no fatigue crack growing during cyclic loading, is essential, especially to determine whether previous traffic loading has produced fatigue damage accumulation or not. However, there is a lack of information concerning fatigue test data in the high-cycle region, i.e. for stress ranges close to the CAFL. Based on full-scale tests an adequate estimate of the CAFL for riveted connections is made by a proposed original method. (3) Web Breathing in Girders with Slender Webs. When a girder with slender web is subjected to in-plane cyclic loading, repeated web buckling deflections (so called: web breathing) may lead to fatigue cracks. Such cracks generally commence at the weld toe of the fillet welds that connect a web to its boundary elements. Four full-scale I-girders with slender webs were laboratory tested. The investigation mainly focused on gaining a better knowledge of the fatigue behaviour of slender girders with relatively large panel aspect ratios and subjected to combined bending and shear. Nonlinear FE-analyses of the test girders were performed to investigate the stress state along the boundary of the web during loading and good agreement with the results of laboratory measurements was found. The risk for fatigue cracking due to web breathing seems to increase with increasing panel aspect ratio. Moreover, web panels subjected to combined bending and shear are more prone to fatigue cracking due to web breathing than similar panels subjected to predominant shear. An analysis of a box section arch railway bridge, where a breathing tendency of some web panels was observed, is also presented. Finally, based on evaluations of experiments a new fatigue design approach for avoiding cracking due to web breathing is proposed.
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| 23. |
- Crocetti, Roberto, et al.
(författare)
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Raka balkar och pelare
- 2016. - 5
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Ingår i: Limträhandbok : Del 2. Projektering av limträkonstruktioner - Del 2. Projektering av limträkonstruktioner. - 9789198030464 ; , s. 53-69
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Bokkapitel (populärvet., debatt m.m.)
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| 24. |
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| 25. |
- Crocetti, Roberto
(författare)
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Snedsågade balkar, krökta balkar och bumerangbalkar
- 2016. - 5
-
Ingår i: Limträhandbok : Del 2. Projektering av limträkonstruktioner - Del 2. Projektering av limträkonstruktioner. - 9789198030464 ; , s. 102-118
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Bokkapitel (populärvet., debatt m.m.)
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| 26. |
- Crocetti, Roberto, et al.
(författare)
-
Strengthening of large diameter singel dowel joints
- 2010
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Rapport (refereegranskat)abstract
- A preliminary study for implementation of a novel truss node is presented. For this purpose, the load-slip behaviour of double-shear loaded single large dowel joints was investigated. Out of a total of 26 laboratory shear tests, 5 were performed on non-reinforced specimens. The remaining 21 tests were performed on specimens reinforced by means of self-tapping screws. All laboratory tests were conducted under monotonic quasi-static loading. The distance between the dowel and the loaded edge of the timber element was considerably smaller than the minimum distance suggested by building codes. The influence of both i) the placement and ii) the diameter of the reinforcing screws on the load-slip behaviour of the joint was studied. The study shows that the scatter in test results is considerably reduced when reinforcing screws are used. The study also shows that the reinforcing screws prevent the joint to fail due to premature splitting. Thus, due to the presence of the reinforcing screws, no reduction of load-carrying capacity of the dowel caused by the short distance between dowel and loaded edge of the timber element needs to be applied. Further, the reinforced specimens exhibited a very ductile load-slip behaviour and - after the first drop in the load-slip curve occurred - the joints still showed a significant reserve of load-carrying capacity.
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| 27. |
- Crocetti, Roberto, et al.
(författare)
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Stress-laminated-timber decks: state of the art and design based on Swedish practice
- 2016
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Ingår i: European Journal of Wood and Wood Products/Holz als Roh - und Werkstoff. - : Springer Science and Business Media LLC. - 1436-736X .- 0018-3768. ; 74:3, s. 453-461
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Tidskriftsartikel (refereegranskat)abstract
- Stress-laminated-timber (SLT) bridge decks area valid alternative to conventional short- and medium-spanbridges in terms of cost and performance. SLT decks aremade from a number of planks or glulam beams positionedside by side and stressed together using high-strength steelbars. A concentrated load can therefore be distributed fromthe loaded beams onto adjacent beams due to the resistingfriction caused by the pre-stressing of all beams in thedeck. This paper describes the state of the art of SLT bridgedecks, with special emphasis on Swedish practice. Theeffect of butt joints on deck deflection and solution appliedto accommodate the loss of pre-stress are shown. Simpledesign tools for the preliminary design of road bridges areillustrated. Best practice with regard to some detailing,water protection and durability is also discussed. Finally,possible developments of SLT bridges are discussed.
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| 28. |
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| 29. |
- Crocetti, Roberto, et al.
(författare)
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Takras avslöjar allvarliga brister
- 2011
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Ingår i: Samhällsbyggaren. - 2000-2408. ; :5, s. 22-27
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- SP har etablerat en databas med 180 rasade eller skadade tak. Det framgår, att det var övervägande stål- och träkonstruktioner, som hade rasat. Endast en skadad betongkonstruktion rapporterades. Byggnadernas ålder spänner över cirka 100 år, men 60 % är uppförda från 1980 och framåt. Taken är förhållandevis flacka. Ca 30 % är lantbruksbyggnader. De dominerande rasorsakerna är dimensioneringsfel och utförandefel. Till dimensioneringsfel räknas bl a, att man inte har dimensionerat över huvudtaget, och att man inte har beaktat snöfickor mm. Detta är några av slutsatserna i den utredning, som SP har utfört tillsammans med Skanska, Lunds tekniska högskola och Lantbruksuniversitetet, och som publicerades den 1 juni 2011.
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| 30. |
- Crocetti, Roberto, et al.
(författare)
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Timber Arch Bridges with V-shaped Hangers
- 2019
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Ingår i: Structural Engineering International. - : Informa UK Limited. - 1016-8664 .- 1683-0350. ; 29:2, s. 261-267
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Tidskriftsartikel (refereegranskat)abstract
- The arch is a very efficient load bearing structure, especially when its shape is affine to the funicular of forces. However, if live loads are predominant as compared to permanent uniformly distributed gravity loads, the arch will be subjected to substantial bending moments, thus losing a great part of its structural efficiency. In traditional arch bridges with hangers arranged in a vertical manner, asymmetrical loads would cause a substantial deviation of the pressure line from the axial line of the arch. In this paper, an innovative concept for timber arch bridges is introduced where V-shaped hangers, rather than vertical hangers, are used. The adoption of V-shaped hangers significantly contributes to the reduction of the eccentricity between the pressure line and the axial line of the arch, thus decreasing the magnitude of bending moments in the arch. The paper discusses the advantages of using V-shaped hangers as an alternative to vertical hangers, both in terms of statics, in-plane stability and dynamic efficiency. Moreover, the design and the recent construction of a parabolic three-hinged arch made of timber, with a steel V-shaped hanger is thoroughly discussed in the paper.
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| 31. |
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| 32. |
- Crocetti, Roberto
(författare)
-
Utformning av limträdetaljer
- 2016. - 5
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Ingår i: Limträhandbok : Del 2. Projektering av limträkonstruktioner - Del 2. Projektering av limträkonstruktioner. - 9789198030464 ; , s. 228-235
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Bokkapitel (populärvet., debatt m.m.)
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| 33. |
- Danielsson, Henrik, et al.
(författare)
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Brittle Failure Modes in Nailed Steel Plate Connections
- 2016
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Ingår i: World Conference on Timber Engineering 2016.
-
Konferensbidrag (refereegranskat)abstract
- This paper deals with theoretical and experimental investigations of nailed steel plate connections. For the experimental part, a total of 43 laboratory tests on connections loaded in tension parallel to the grain are reported. The paper deals also with finite element analysis of the connection, presenting a study on the 3D stress distributions within the wood member and a study of the progressive wood fracture course by the use of a 3D nonlinear fracture mechanics model, more precisely a cohesive zone model. Results of the experimental tests are compared to results of the numerical analyses and to strength predictions according to Eurocode 5. The comparison between theoretical and experimental results indicate that the Eurocode 5 design approach for plug shear failure in nailed steel plate connections might be nonconservative in relation to predicted strength values. Also failure modes predicted by Eurocode 5 are often erroneous. Results of the numerical analyses indicate that load eccentricity has a major influence on the connection strength.
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| 34. |
- Debertolis, Mattia, et al.
(författare)
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Investigation on mechanical connections with birch plywood gusset plates
- 2023
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Ingår i: 19th Annual Meeting of the Northern European Network for Wood Science and Engineering. - Ås, Norway : The Nordic Forest Research Cooperation Commitee. ; , s. 96-98
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Konferensbidrag (refereegranskat)abstract
- The construction industry is increasingly driven by sustainability concerns, prompting a search for alternative materials with a low environmental footprint, such as engineered wood products. Nowadays, connections of timber elements are still performed by the use of steel plates. However, steel plates can be replaced by plywood made of birch since it has superior mechanical properties compared to plywood made from softwood (Wang et al. 2021, 2022; Crocetti et al. 2021; Werner Åström, 2019). Besides, the capacity calculation for this connection according to the standards is conservative, meaning that the efficiency is low and the actual capacity could be much higher than the design value (Rossi et al. 2016). This research aims to enhance the knowledge and the design process of timber-to-timber connections with birch plywood (BP) plates.
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| 35. |
- Edlund, Bo, 1936, et al.
(författare)
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Bridge expansion joints -- design for movements, performance and durability
- 2007
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Ingår i: IABSE Symposium Weimar 2007 "Improving Infrastructure Worldwide"; Report, IABSE Zürich. - 9783857481161 ; , s. 302--303-
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Konferensbidrag (refereegranskat)abstract
- Expansion joints in medium-size and long bridges should be regarded as important bridge components.There is a trend to minimize the number of joints, and design each joint to permit large movements. It is therefore important to develop suitable joint types that function smoothly for such large movements during a long time without damages or malfunctioning. A widely used, modern joint type for large joint movements is the Modular Bridge Expansion Joint (MBEJ). The paper mainly deals with different aspects of MBEJs (function, fatigue, durability, maintenance, noise etc). Traffic forces on MBEJs as well as quality requirements and assessment are discussed.
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| 36. |
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| 37. |
- Ekholm, Kristoffer K J, 1982, et al.
(författare)
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Full-Scale Ultimate-Load Test of a Stress-Laminated-Timber Bridge Deck
- 2012
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Ingår i: Journal of Bridge Engineering. - 1084-0702 .- 1943-5592. ; 17:4, s. 691-699
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Tidskriftsartikel (refereegranskat)abstract
- A general assumption reported in the literature is that the structural response of a stress-laminated-timber (SLT) bridge deck islinear until failure. However, few studies of ultimate-load tests (ULTs) on timber bridges have been reported. A full-scale test of a SLT deck(span, 4.9 m; thickness, 270 mm) was performed to obtain the deformations at various prestress levels as well as at the ultimate-load capacityof such a structure. Prior to the ULT, nondestructive tests (NDT) were performed at three different prestress levels. The load was applied as anaxle load positioned both centrically and eccentrically. The deflections were about 10% larger at a prestress level of 300 kPa compared with aprestress level of 600 and 900 kPa. For applied loads larger than 150–250 kN, the deflection of the deck was nonlinear at certain positions.This was most likely owing to large concentrated shear forces that resulted in interlaminar slip between the laminates. The limit for linearityseems to be dependent on the applied prestress. A prestress of 600 kPa and an eccentrically positioned load was used for the ULT. Failureoccurred at a load level of 900 kN. The existing design codes and new procedures in development may be verified and calibrated against theresults in this paper.
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| 38. |
- Ekholm, Kristoffer K J, 1982, et al.
(författare)
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Mechanical Properties of Stress Laminated Timber Decks – Experimental study
- 2009
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Ingår i: CIB-W18 Proceedings meeting forty-two 2009, Dübendorf, Switzerland. - 1864-1784.
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Konferensbidrag (refereegranskat)abstract
- In several European countries, the design of stress laminated bridges has been conducted according to a simplified method developed by M. A. Ritter in the 1990’s, valid for American wood species such as Douglas fir. According to this method a stress laminated deck can be designed as a beam with cross section dimensions beff x t, where beff is a fictitious (or effective) width - determined according to orthotropic plate theory - and t is the thickness of the deck. However, there are several uncertainties concerning the validity of this model concerning its application to European stress laminated bridges. These uncertainties are related to: (1) wood species - in Europe boards or glulam of Norway spruce or Scots pine are generally used; (2) design philosophy - Ritter’s model was developed according to the “allowable stresses design method”, whilst the philosophy behind the Eurocodes is the design method according to the ultimate limit states.In this paper, an experimental investigation on specimens manufactured with pre-stressed glulam will be presented. The glulam is made from Norway spruce. The aim of the study is to estimate the mechanical properties of stress laminated timber decks with varying pre-stressingforces. The methods for measuring (a) transversal modulus of elasticity ET , and (b) the transverse shear modulus GLT will be presented. Comparison with results obtained by this research and results obtained by other researcher will be shown.
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| 39. |
- Ekholm, Kristoffer K J, 1982, et al.
(författare)
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Stress-Laminated Timber Decks Subjected to Eccentric Loads in the Ultimate Limit State
- 2013
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Ingår i: Journal of Bridge Engineering. - 1084-0702 .- 1943-5592. ; 18:5, s. 409-416
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Tidskriftsartikel (refereegranskat)abstract
- Stress-laminated timber (SLT) bridge decks are generally designed using either linear hand calculation methods or linear finite-element models. Several studies have shown, however, that the behavior of SLT decks is nonlinear when loaded until failure. In this paper, several linear design methods are compared with one another and with an ultimate load test of a full-scale SLT deck subjected to an eccentric load. Some of the linear hand calculation methods show significant discrepancies in results, depending on the load position. There are also variations in the results from finite-element models, depending on the material properties assigned to the deck. All the design methods failed to predict the deflection of the tested deck when loaded to failure. A larger deflection was observed in the full-scale test than that predicted by the design methods. As a result, the linear design method could underestimate the bending stresses in the deck. Several hand calculation methods are also unable to calculate the transverse forces and moments necessary for design according to Eurocode 5.
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| 40. |
- Ekholm, Kristoffer K J, 1982, et al.
(författare)
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Ultimate limit state load test of stress-laminated-timber deck
- 2010
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Ingår i: World conference on timber engineering 2010, June 20-24 2010, Riva del Garda, Italy. - 9781622761753 ; 700:2, s. 343-352
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Konferensbidrag (refereegranskat)abstract
- Glulam beams made of Norway spruce are stressed together with high strength steel bars creating a Stress laminated timber deck (SLTD). Deflections and stresses can be estimated with both finite element models based on orthotropic plate theory as well as with simplified hand calculation methods based simple beam theory. If SLTDs areloaded until failure in the ultimate limit state (ULS), phenomena which generally do not occur in serviceability limit state (SLS) must be taken into account. Slip will occur in the interlaminar surface between the stressed glulam laminations. Once slip has occurred, stress will redistribute between the laminations. A rectangular SLTD was tested for several load levels and pre-stress levels. Deflections were compared with a finite element orthotropic model. These results were also compared with several established design methods. After failure occurred in the ULS, the load was first removed and then applied again, in order to emphasize the reliability of stress redistribution within SLTD.
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| 41. |
- Fernandez-Cabo, Jose L., et al.
(författare)
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Assessment of wire-frame analysis models of a historical planked timber arch
- 2015
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Ingår i: Proceedings of the Institution of Civil Engineers. - : Thomas Telford Ltd.. - 0965-0911 .- 1751-7702. ; 168:9, s. 680-694
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes theoretical and experimental work undertaken to obtain a structural model for assessment of historical Latin-American vertically laminated planked timber arches, as built by the Spanish, mainly in the seventeenth and eighteenth centuries. Many such arches still stand, and represent an important historical heritage. Following initial historical and construction studies, a structural analysis is being undertaken; the first stage is described here. Two wire frame analysis models are developed and assessed: a finite-element model using elasto-plastic constitutive equations (implemented in SAP2000), and another model using limit analysis. An experimental programme is also conducted. The structure presents elasto-plastic behaviour with an important plastic range, which is a relevant and favourable property for a structure. The numerical elasto-plastic model shows good agreement with experimental results for the elastic range and deviations around 60% for the plastic range. The plastic model shows a deviation of around 40%, which is an important outcome at this stage. The models show the key problem of the structure: the transference of the bending moment along planks is poor, restricting its overall load-bearing capacity. Additional tests and more complex material models (including failure in tension perpendicular to the grain), using two-dimensional and three-dimensional finite elements, are now under development to recalibrate the models presented.
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| 42. |
- Furuheim, E., et al.
(författare)
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Connections for post and beam glulam structures using birch plywood plates and screws
- 2021
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Ingår i: World Conference on Timber Engineering 2021, WCTE 2021. - : World Conference on Timber Engineering (WCTE).
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Konferensbidrag (refereegranskat)abstract
- Multi-storey timber buildings can be built adopting a post and beam system made of glulam. A typically adopted connection for such structures is that which make use of slotted-in steel plates and dowels. Even though such a type of connection is able to transfer large loads, it has a number of deficiencies. Besides being relatively costly in terms of both materials and manufacturing, connections with slotted-in steel plates and dowels requires a very high level of accuracy both in manufacture and in construction. By replacing steel plates and dowels with gusset plates of e.g. plywood and screws, respectively, there are a number of possible benefits including ease of manufacture, economy and environmental issues. This paper presents a comprehensive experimental investigation on the load bearing capacity of post-beam connection consisting of slotted-in plywood plates in combination with either full-threaded self-tapping screws or small-diameter dowels. The investigation also includes a study on the influence of the plywood plate's orientation in relation to the direction of load. Test results and hand calculations have confirmed that beam-column connections with gusset plates of birch plywood, may reach sufficient capacities for realistic design in the Ultimate Limit State (ULS). By utilizing both external and slotted-in gusset plates of plywood, one could reach the same capacity and stiffness as a slotted-in steel plate connection. To further reduce the amount of steel in the connections, results showed that prefabricated glued columns with plywood can be an opportunity.
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| 43. |
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| 44. |
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| 45. |
- Gottsäter, Erik, et al.
(författare)
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Comparison of Models for the Design of Portal Frame Bridges with Regard to Restraint Forces
- 2017
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Ingår i: Structures Congress 2017, Denver, United States, 6-8 April 2017. - Reston, VA : American Society of Civil Engineers. - 9780784480403 ; , s. 326-339
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Konferensbidrag (refereegranskat)abstract
- In the design of concrete bridges an important aspect is limiting crack widths, since large cracks can lead to e.g. corrosion and affect the bridge functionality. Restraint forces caused by thermal loads and shrinkage will likely constitute a large part of the total forces acting on the bridge in crack width design. In this paper, restraint stresses in portal frame bridges are calculated according to Eurocode with simple hand calculation models, 2D frame models and linear elastic 3D FE-models. The results are then compared and used in Eurocode crack width design methods. Large tensile restraint stresses were found in the transverse direction close to the frame corners, and the required reinforcement amount significantly exceeded the minimum reinforcement prescribed by codes. The results are however unrealistic since the thermal load distribution is simplified, and the crack width formula does not take the reduction of restraint stresses due to cracking into account. Future studies shall therefore determine a more realistic thermal load distribution and the effects of cracking, in order to create a more accurate linear elastic 3D FE design method.
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| 46. |
- Gottsäter, Erik, et al.
(författare)
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Simulation of thermal load distribution in portal frame bridges
- 2016
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Ingår i: IABSE Congress Stockholm, 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment.
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Konferensbidrag (refereegranskat)abstract
- Uneven exposure to e.g. solar radiation can cause temperature differences between various structural parts of a bridge, which leads to tensile stresses if the parts cannot move freely. In this study, thermal simulations and stress calculations on a model of a portal frame bridge are performed with the aim of evaluating the temperature difference between the bridge parts. It is shown that the temperature difference between parts which is proposed by Eurocode 1 is overestimated, thus the resulting stress distribution being unrealistic. Using the design method proposed by Eurocode 1 is therefore likely to exaggerate the required reinforcement in crack width limit design, which in turn would lead to unnecessary costs and environmental impacts. Further studies are needed in order to determine proper thermal load values and temperature distributions.
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| 47. |
- Gottsäter, Erik, et al.
(författare)
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Simulation of thermal load distribution in portal frame bridges
- 2017
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Ingår i: Engineering Structures. - : Elsevier BV. - 1873-7323 .- 0141-0296. ; 143, s. 219-231
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Tidskriftsartikel (refereegranskat)abstract
- Uneven exposure to e.g. solar radiation can cause temperature differences between various structural parts of a bridge, which leads to tensile stresses if the parts cannot move freely. In this study, thermal simulations and stress calculations on a model of a portal frame bridge are performed with the aim of evaluating the temperature difference between the bridge parts. Factorial design is used in a parametric study to determine the influence of different factors on the temperature difference and the largest reasonable temperature difference obtainable for the chosen weather data. The study shows that the quasi-permanent temperature difference between parts which is proposed by Eurocode 1 is overestimated, causing tensile stresses in the transverse direction to be exaggerated significantly. Using the design method proposed by Eurocode 1 is therefore likely to overestimate the required reinforcement in crack width limit design, which in turn would lead to unnecessary costs and environmental impacts. The results also indicate that the temperature distribution within the bridge is different from what is given in Eurocode load cases, and consequently, the largest tensile stresses appear in other areas of the bridge. A simplified temperature distribution is therefore investigated and shown to give similar results as the detailed thermal simulations.
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| 48. |
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| 49. |
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| 50. |
- Hallak Neilson, John, et al.
(författare)
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Dynamic properties of two pedestrian wooden bridges including seasonal effects
- 2020
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Ingår i: Proceedings of the International Conference on Structural Dynamic , EURODYN. - : European Association for Structural Dynamics. ; , s. 1805-1813
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Konferensbidrag (refereegranskat)abstract
- The dynamic properties of two pedestrian wooden bridges situated in the Stockholm area have been determined experimentally. The main purpose was to investigate if these properties are season dependent. For that, tests were performed during the winter and the spring. 17 accelerometers were used to measure both vertical and horizontal vibrations. An impact hammer was used to excite the bridges. For the Vega bridge, a large variation for the lowest natural frequencies was observed, both for the first vertical and for the first transversal mode. For the Hägernäs bridge, a large variation was observed for the first transversal mode but not for the first vertical mode. With exception for the first transversal mode for the Hägernäs bridge, no significant differences regarding the damping between winter and spring were observed. Finite element models of the two bridges have also been implemented and a good agreement with experimental results have been obtained. The numerical models have shown that the connections between the different components of the bridges have a significant influence on the dynamic properties. The models have also shown that the variation of the stiffness for the asphalt layer may explain the differencies for the natural frequencies between spring and winter. However, due to the incertainties in the modelling of the asphalt, this conclusion must be taken with caution.
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