Papers by Roberto Crocetti
Proceedings of the World Congress on Civil, Structural, and Environmental Engineering, 2016
Large spans structures should ideally be designed so that they work primarily in tension and/or c... more Large spans structures should ideally be designed so that they work primarily in tension and/or compression. In fact, minimizing bending moments leads in general to an optimum utilisation of the structure, regardless what material is chosen. This often results in slender and elegant shapes. Timber is a structural material which has excellent strength and stiffness, in particular when these properties are expressed in specific terms. By specific strength and specific stiffness, it is meant the material strength and the material Young's modulus, respectively, divided by its density. As an example, it can be mentioned that both the specific strength and the stiffness in tension and compression parallel to the grain of e.g. spruce timber are even superior to that of a common carbon steel. For this reason, timber is a material which is particularly appropriate for large span structures. This paper gives a description of both traditional and innovative structural shapes which can be used for large buildinsg with timber as main load bearing material. Emphasis is put on planar structures; however, a brief discussion on spatial structures will also be presented. As spans become longer, a number of problems arises. For example, as compression members get longer, buckling begins to be an issue. Moreover, most likely large-span structures will be made of several members, which must be prevented from coming apart at the joints. In this paper, methods to reduce the risk for both in-plane and out-of-plane buckling of timber members are illustrated. Also, suitable joints able to resist either large compression and tension forces are presented and discussed.
Construction and Building Materials
Bridge Maintenance, Safety, Management, Resilience and Sustainability
The general assumption in stress-laminated-timber (SLT) bridge design is that the structural resp... more The general assumption in stress-laminated-timber (SLT) bridge design is that the structural response is linear both in the serviceability limit state (SLS) and in the ultimate limit state (ULS). However, this has been shown not to be the case according to a full-scale test performed in Sweden where the SLT deck was subjected to a failure load. When an SLT deck is loaded to failure, non-linear behaviour must be considered when a structure of this kind is analysed. Both horizontal and vertical slip occur in the interlaminar interface between the stressed glulam laminations. This behaviour does not occur in a solid timber plate. Once slip has occurred, the stresses are redistributed between the laminations. Interlaminar slip is of great importance and is affected by several factors such as the pre-stress level, surface roughness and surface moisture content. A rectangular SLT deck, 5.00 × 7.98 × 0.27 m 3 (length, width and thickness), with two patch loads positioned close to the edge, was tested. The deflection values for both ultimate and non-destructive loads were compared with finite element (FE) models of the SLT deck in order to evaluate the behaviour of the deck. The results from the experiments were compared with both linear and non-linear FE models.
XI International Conference on Structural Dynamics
Wind-induced dynamic excitation is becoming a governing design action determining size and shape ... more Wind-induced dynamic excitation is becoming 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 failure. Although some TTBs have been instrumented and measured 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 provide key elements to FE modelers.
The torsional bracing system is a fundamental part of a bridge structure that provides torsional ... more The torsional bracing system is a fundamental part of a bridge structure that provides torsional restraint to the steel girders and prevents lateraltorsional buckling of the main girders during construction phase when no lateral restraint, in form of the continuous concrete deck, is yet provided to the compressive flanges. This paper investigates the performance of conventional discrete torsional braces of seven randomly chosen Scandinavian steel-concrete composite bridges.
The limiting factors when it comes to design of timber structures are often stiffness properties ... more The limiting factors when it comes to design of timber structures are often stiffness properties of timber products. The stiffness requirements in serviceability limit state, both short-term and longterm deformation especially in horizontal members, is a factor that often makes it necessary to increase the dimensions of the member. Both the results from experimental studies and the results of analytical modelling are presented. The experimental study comprises results from short-term tests to failure of nine glulam beams strengthened with bonded steel plates or CFRP laminates and mechano-sorptive creep tests of strengthened glulam lamellas loaded in bending at 8 MPa. Positive effects on the strengthening when it comes to short-term and long-term behaviour were shown. The arrangement of the reinforcement in the cross-section makes it possible to control the behaviour of the beams in terms of strength, stiffness and ductility. The experimental results agreed very well with the propose...
The TRE3 research project focuses on the development of a new and innovative timber frame wall mo... more The TRE3 research project focuses on the development of a new and innovative timber frame wall modulus for emergency housing facilities. The wall modulus, in this paper referred to as Hybrid Timber Frame (HTF) wall system, is an evolution of the traditional Light-Frame Timber (LFT) structural systems and combines the advantages and some peculiar aspects of lightweight structures to the potentialities of Cross-Laminated Timber (CLT) panels. This hybrid approach makes the HTF structural system suitable for the production of light and high-performing wall moduli, allowing an advanced prefabrication process, fast assembling procedures and a simple disassembly. The paper provides a description of the HTF wall system following a multidisciplinary approach. Particular attention is paid to the mechanical and geometrical characterisation of three HTF wall moduli, used to assemble different housing units. The structural design is carried out by considering severe loading conditions (which inc...
International Journal of Civil Engineering, 2021
This paper deals with experimental and numerical dynamic analyses of two timber footbridges. Both... more This paper deals with experimental and numerical dynamic analyses of two timber footbridges. Both bridges have a span of 35 m and consist of a timber deck supported by two timber arches. The main purpose is to investigate if the dynamic properties of the bridges are season dependent. To this end, experimental tests are performed during a cold day in winter and a warm day in spring in Sweden. The first bending and transverse mode frequencies increase 22% and 44%, respectively, due to temperature effects in the case of Vega Bridge. In the case of Hägernäs bridge, the corresponding values are 5% and 26%. For both bridges, the measured damping coefficients are similar in winter and spring. However, the damping coefficients for the first bending and transverse modes are different for both footbridges: about 1% for the Hägernäs bridge and 3% for the Vega bridge. Finite-element models are also implemented. Both numerical and experimental results show good correspondence. From the analyses ...
Construction and Building Materials, 2019
h i g h l i g h t s Experiments were performed on notched connections and CLT-concrete composite ... more h i g h l i g h t s Experiments were performed on notched connections and CLT-concrete composite floors. Analytical method based on c-method is suitable for CLT-concrete composite floors. 3D FE-models for notches and composite floors were developed and validated. Influence of notch depth on connections and composite floors were investigated.
BioResources, 2016
The key point of design for timber-concrete composite structure is to ensure the reliability of s... more The key point of design for timber-concrete composite structure is to ensure the reliability of shear connectors. This study examined the mechanical properties of bolt-type connectors in timber-concrete composite structures theoretically and experimentally. The theoretical study was based on the Johansen yield theory (European Yield Model). Push-out specimens with different bolt dimensions were tested to determine the shear capacity and slip modulus. According to the experimental results, bolts yielded without timber or concrete cracks when the stiffness of bolts was not very great. The shear capacity and slip modulus of the bolt connectors were directly proportional to the diameter of the bolt. The strength of concrete was found to significantly affect the shear capacity of bolt connectors. Comparison between the theoretical and the experimental shear strength results showed reasonable agreement.
Structures, 2016
This paper deals with theoretical and experimental investigations of nailed steel plate connectio... more This paper deals with theoretical and experimental investigations of nailed steel plate connections. For the experimental part, a total of 99 laboratory tests have been carried out in order to study failure mechanism and shear capacity of nailed steel plate connections. The testing programme comprised two nail lengths, two steel plate thicknesses and five nailing patterns. All tests related to loading of the plate in the direction of the grain of the wood. The nail patterns were designed to give ductile joint failure by yielding of the nails and/or bearing failure of the wood. The failure load was recorded and the mode and course of failure noted. For some of the specimens, deformation of the nails during loading was studied by means of an X-ray equipment. Deviations between the test results and contemporary consensus as manifested in the SS-EN 1995-1-1:2004 and the Johansen theory for ductile failure were found in several respects: development of the plastic hinges in the nails, influence of nail length, steel plate thickness and nail-to-nail and edge distances. The paper also presents an empirical equation based on multiple regression analysis of the test results was proposed as an attempt to predict the load-carrying capacity of nailed connections in shear.
Journal of Bridge Engineering, 2017
Steel girders require stability controls for different construction stages before the lateral-tor... more Steel girders require stability controls for different construction stages before the lateral-torsional support from the concrete deck occurs. The load-carrying capacity of bridge girders and bracing forces generated in their bracings are very sensitive to the girders' initial imperfections in terms of both the magnitude and distribution along the span. Relatively little knowledge is available in this matter; however, decisions on the "worst" shape of imperfections that gives a conservative resistance and/or maximizes the bracings forces is often not an easy task in practice. The present paper reports the test results (in terms of the load-carrying capacities and bracing forces) of a large-scale bridge of twin I-girder type in which the location of the intermediate cross beam was varied across the depth of the main girders. Moreover, extensive numerical investigations were performed to study the effects of some relevant shape of imperfections on both the load-carrying capacities of the studied bridges and the magnitude of bracing forces generated in the cross beams that were involved. The test results showed that the load-carrying capacity of steel girders can exceed their lowest theoretical eigenvalue because of the presence of initial imperfections. In the finite-element analyses of the studied bridge cases, in some cases, the girders followed their shape of geometric imperfections and reached a load value that was greater than the lowest eigenvalue of the systems.
Structures, 2016
Finite-element programs can be used for designing columns and their bracing systems. It is well k... more Finite-element programs can be used for designing columns and their bracing systems. It is well known, however, that the output obtained from such programs is highly dependent upon the input (such as imperfections and stiffness properties). In the present study, the effects of imperfections on the predicted strength and stiffness requirements of steel columns and of their bracing systems are investigated. Two different systems are analyzed: 1) a braced non-sway column and 2) a braced sway column. It was found that a poor choice of the shape of the initial imperfections can provide unrealistic results in terms of both the buckling load on the columns and the predicted reactions of the bracings. It was also found that superimposing different imperfection shapes can contribute to obtaining realistic and trustworthy results. Furthermore, it was shown that the shapes of the initial imperfections that lead to the lowest buckling load and those that result in the strongest bracing forces, are generally not the same.
Engineering Structures, 2016
The competitiveness of timber as structural material in large structures is often governed by the... more The competitiveness of timber as structural material in large structures is often governed by the cost of structural joints. Tests indicate that the new joint concept presented herein using glued wood-to-steel plate joints can possibly reduce the cost by matching joint strength to member strength. The design is inspired by two previously proposed designs using a single large dowel and using a rubber foil interlayer in adhesive joints. Analytical 1D and numerical 3D models of the bond line are proposed in order to further develop the concept, both in the case of a traditional adhesive joint and for the innovative rubber foil adhesive joint. The glued wood-to-steel plate joints studied are lap joints with a load bearing capacity assumed to be governed by failure within or along the bond line. In the 1D and 3D structural models both linear elastic and non-linear fracture mechanics were applied, with the non-linear fracture mechanics model taking into account the gradual damage fracture softening in a fracture zone. For the conventional type of bond line it was found that bond line softening needs to be considered for adequate strength analysis while it was not needed for a bond line with a rubber foil. The computational results are compared to previous full scale test results. The numerical results show good agreement and the analytical results reasonable agreement. When using a high strength adhesive, the strength of the wood along the bond line is governing joint failure. For this case, the analyses predict a 150% load bearing capacity increase by the introduction of a rubber foil as compared to a traditional design. The test results indicated an even higher increase.
Sanhallsbyggaren, 2011
Under perioden januari till mars 2010 rasade ett stort antal tak i samband med kraftiga snöfall. ... more Under perioden januari till mars 2010 rasade ett stort antal tak i samband med kraftiga snöfall. Utmärkande var att det var minusgrader under hela snöfallsperioden, och att det blåste en övervägande nordlig till ostlig vind. Försäkringsbolagen har uppgivit, att man fick skade anmälningar från mer än 3000 byggnader.
European Journal of Wood and Wood Products, 2015
Stress-laminated-timber (SLT) bridge decks are a valid alternative to conventional short-and medi... more Stress-laminated-timber (SLT) bridge decks are a valid alternative to conventional short-and medium-span bridges in terms of cost and performance. SLT decks are made from a number of planks or glulam beams positioned side by side and stressed together using high-strength steel bars. A concentrated load can therefore be distributed from the loaded beams onto adjacent beams due to the resisting friction caused by the pre-stressing of all beams in the deck. This paper describes the state of the art of SLT bridge decks, with special emphasis on Swedish practice. The effect of butt joints on deck deflection and solution applied to accommodate the loss of pre-stress are shown. Simple design tools for the preliminary design of road bridges are illustrated. 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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Papers by Roberto Crocetti