Roberto Crocetti

Innovative Timber-Concrete Composite Structures with Prefabricated FRC Slabs

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 experiments 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

Full-Scale Ultimate-Load Test of a Stress-Laminated-Timber Bridge Deck

A general assumption reported in the literature is that the structural response of a stress-laminated-timber (SLT) bridge deck is linear 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 capacity of such a structure. Prior to the ULT, nondestructive tests (NDT) were performed at three different prestress levels. The load was applied as an axle load positioned both centrically and eccentrically. The deflections were about 10% larger at a prestress level of 300 kPa compared with a prestress 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 linearity seems to be dependent on the applied prestress. A prestress of 600 kPa and an eccentrically positioned load was used for the ULT. Failure occurred at a load level of 900 kN. The existing design codes and new procedures in development may be verified and calibrated against the results in this paper.

An Innovative Prefabricated Timber-Concrete Composite System

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° 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° 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° 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.

Stress-Laminated Timber Decks Subjected to Eccentric Loads in the Ultimate Limit State

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.

Comparison of Models for the Design of Portal Frame Bridges with Regard to Restraint Forces

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.

Scaffolding Bracing of Composite Bridges during Construction

Relatively little bracing of steel girders can significantly reduce possible risk of buckling failures, before the composite action between steel and concrete occurs. This paper intended both experimentally and numerically, to study the torsional bracing performance of a typical type of scaffoldings commonly used in bridge construction. Minor improvements in the structure of the scaffoldings as well as at their connections with steel girders were needed for this purpose, which are shortly discussed in this paper. In the numerical investigations, the effects of different initial imperfections on bracing properties of the scaffoldings were also investigated. The study was extended to different bridge lateral torsional buckling slenderness ratios, and geometries. Results showed that the proposed system greatly increased the load carrying capacity of the studied bridges with consideration of lateral torsional buckling during construction phase. Brace forces created in the scaffolding trusses were also measured both in the experimental and in the numerical investigations. Finally, indications of brace moment versus in-plane moment values for different magnitudes of initial imperfections and lateral torsional buckling slenderness ratios were given. (Less)

End-Warping Bracings during the Construction of Steel Bridges

AbstractSlight bracing of steel bridges to control end warping of the compression flanges near the end supports can be very effective in enhancing the load-carrying capacity of the main girders that are involved. Relatively little information is available, however, regarding the stiffness and strength requirements of end-warping bracings. The results of seven large-scale laboratory tests of different configurations of bracings, including plan bracing and corrugated metal sheets, used in a twin I-girder bridge to resist end warping at support points are presented here. Bracing forces generated in the plan bracings of the test bridge were also compared with those obtained through an approximate analysis for the preliminary analysis of such bracings. Moreover, the bracing forces present in the cross beam of the test bridge were obtained for the different end-warping brace configurations that were investigated. The bracings, the plan bracing type and corrugated metal sheets, were found to effectively enhance ...

Prefabricated timber-concrete composite floors

The presented investigation concerns the study of novel types of timber-concrete composite floors, manufactured with “dry connections” (Crocetti et al. In: 11th WCTE, Riva del Garda: international conference proceeding of 11th WCTE, Riva del Garda, 2010; In: RILEM 2013: Materials and Joints in Timber Structures—Recent Advancement of Technology Stuttgart, Germany, 2013: RILEM 2013, Stuttgart, 2013; Sartori et al. In: Enhance mechanical properties of timber, engineered wood products and timber structures. University of Bath, COST FP1004, Zagreb, 19 April 2012, 2012). Three full-scale nominally identical floor elements were investigated. The shear connector system used in the investigation was realized by means of self-tapping screws driven at an angle of 45° into the wood. First, the screws were inserted on the top of the glulam beams. Then, the beams were twisted upside-down and placed on concrete formwork (Fragiacomo In: Struct Eng Mech 20(2):173–189, 2005). Then fibre reinforced concrete (FRC) was cast in the formwork. Quasi-static bending tests and long-term bending test were performed. It was found that the proposed connection systems performed more than satisfactory in the short term, showing a very high degree of composite action even at load levels close to the failure load. However, long-term loading (Fragiacomo and Ceccotti In: J Struct Eng 132(1):13–22, 2006) induces increased deformation, which should be taken into account in SLS design.

Stress-laminated-timber decks : state of the art and design based on Swedish practice

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.

Bridge Expansion Joints – Design for Movements, Performance and Durability

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.