The research presented in this thesis is to evaluate the feasibility of demountable shear connectors as an alternative to welded shear connectors in composite structures through push off tests and composite beam tests. Push off tests were conducted to examine the shear strength, stiffness and ductility of demountable shear connectors in composite structures. The experimental results showed that demountable shear connectors in composite structures have very similar shear capacity to welded shear connectors. The shear capacity was compared against the prediction methods used for the welded shear connections given in Eurocode 4 and AISC 360-10 and the methods used for bolted connections in Eurocode 3 and ACI 318-08. It was found that the AISC 360-10 and ACI 318-08 methods overestimated the shear capacity in some cases. The Eurocode method is conservative and can be utilised to predict the shear capacity of demountable connectors in composite structures. The experimental studies of two identical composite beams using demountable shear connectors and welded shear connectors showed very similar moment capacity. However, the specimen with demountable shear connectors was more ductile compared to the welded specimen. The experimental study suggests that the methods available in Eurocode 4 and BS 5950 for predicting moment capacity and mid span deflection can be adopted for composite beam with demountable shear connectors. In addition, a finite element analysis of push off test and beam test with demountable shear connectors was also conducted for parametric studies and results are used to evaluate the behaviour of composite structures.

The research presented in this thesis is to evaluate the feasibility of demountable shear connectors as an alternative to welded shear connectors in composite structures through push off tests and composite beam tests. Push off tests were conducted to examine the shear strength, stiffness and ductility of demountable shear connectors in composite structures. The experimental results showed that demountable shear connectors in composite structures have very similar shear capacity to welded shear connectors. The shear capacity was compared against the prediction methods used for the welded shear connections given in Eurocode 4 and AISC 360-10 and the methods used for bolted connections in Eurocode 3 and ACI 318-08. It was found that the AISC 360-10 and ACI 318-08 methods overestimated the shear capacity in some cases. The Eurocode method is conservative and can be utilised to predict the shear capacity of demountable connectors in composite structures. The experimental studies of two identical composite beams using demountable shear connectors and welded shear connectors showed very similar moment capacity. However, the specimen with demountable shear connectors was more ductile compared to the welded specimen. The experimental study suggests that the methods available in Eurocode 4 and BS 5950 for predicting moment capacity and mid span deflection can be adopted for composite beam with demountable shear connectors. In addition, a finite element analysis of push off test and beam test with demountable shear connectors was also conducted for parametric studies and results are used to evaluate the behaviour of composite structures. / EPSRC and the University of Bradford

Yes / Steel-concrete composite structures are commonly used in buildings and bridges because it takes advantage of tensile strength of steel and compressive strength of concrete. The two components are often secured by shear connectors such as headed studs to prevent slippage and to maintain composite action. In spite of its popularity, very little research was conducted on steel-concrete composites particularly on headed stud shear connectors in regards to its post-fire behaviour. This research investigates the post-fire behaviour of innovative shear connectors for composite steel and concrete. Three type of connectors were investigated. They are headed stud shear connectors, Blind Bolt 1 and Blind Bolt 2 blind bolts. Push-out test experimental studies were conducted to look at the behaviour and failure modes for each connector. Eighteen push tests were conducted according to Eurocode 4. The push test specimens were tested under ambient temperatures and post fire condition of 200˚C, 400˚C and 600˚C. The results in ambient temperature are used to derive the residual strength of shear connectors after exposing to fire. Findings from this research will provide fundamental background in designing steel-concrete composites where there is danger of fire exposure.

No

Yes / Steel is a highly versatile and 100% recyclable material but is also carbon and energy intensive in production. Steel framed structures are inherently adaptable and potentially demountable. Reuse instead of the common practice of recycling steel by melting, makes good environmental sense, saving both on resources and carbon emissions. Reuse is commercially and technically viable, as demonstrated by isolated projects. Although steel reuse has been identified as an effective method to reduce the carbon and energy impact of construction, it is in effect only marginally used in practice. We found that although there is a sufficient spread between the price of steel scrap and new steel, this difference cannot be captured by the demolition contractors. In steel multi-storey high-rise building structures, composite construction is the most efficient and economic forms of construction. Composite beams incorporate composite floors with profiled steel sheeting are the most common structural system used in multi-storey high-rise buildings and is seen as one of the most important ways of expanding the use of steel buildings in Europe, i.e. increasing market share. However, in terms of reuse, current composite construction systems require extensive cutting on-site during the demolition process making reuse not viable. This paper presents an innovative composite system that is designed for deconstruction and reuse, its structural behaviour and failure modes were observed and analysed through a series of experimental studies and numerical simulation. The results showed that the structural behaviour of this new form of composite system not only allows for deconstruction and reuse, it has a similar structural performance to the traditional composite system with welded shear connectors.

A bridge with precast bridge deck panels was built at the Virginia Tech Structures Laboratory to examine constructability issues, creep and shrinkage behavior, and strength and fatigue performance of transverse joints, different types of shear connectors, and different shear pocket spacings. The bridge consisted of two AASHTO type II girders, 40 ft long and simply supported, and five precast bridge deck panels. Two of the transverse joints were epoxied male-female joints and the other two transverse joints were grouted female-female joints. Two different pocket spacings were studied: 4 ft pocket spacing and 2 ft pocket spacing. Two different shear connector types were studied: hooked reinforcing bars and a new shear stud detail that can be used with concrete girders. The construction process was well documented. The change in strain in the girders and deck was examined and compared to a finite element model to examine the effects of differential creep and shrinkage. After the finite element model verification study, the model was used to predict the long term stresses in the deck and determine if the initial level of post-tensioning was adequate to keep the transverse joints in compression throughout the estimated service life of the bridge. Cyclic loading tests and shear and flexural strength tests were performed to examine performance of the different pocket spacings, shear connector types and transverse joint configurations. A finite element study examined the accuracy of the AASHTO LRFD shear friction equation for the design of the horizontal shear connectors. The initial level of post-tensioning in the bridge was adequate to keep the transverse joints in compression throughout the service life of the bridge. Both types of pocket spacings and shear connectors performed exceptionally well. The AASHTO LRFD shear friction equation was shown to be applicable to deck panel systems and was conservative for determining the number of shear connectors required in each pocket. A recommended design and detailing procedure was provided for the shear connectors and shear pockets. / Ph. D.

The behavior and strength of welded shear studs are subjects of ongoing study. In recent years, research has shown that the American Institute of Steel Construction (AISC) specification equations for shear stud strength are unconservative for studs placed in deck with ribs transverse to the steel beam. Twenty-four solid slab push-out tests, 93 composite slab push-out tests, and bare stud tests were performed to study the effects on stud strength of friction, normal load, position of studs in the ribs of steel deck, concrete strength, and stud properties. Stud diameters ranged from 3/8 in. to 7/8 in., deck heights ranged from 2 in. to 6 in., and both single and pairs of studs were tested. The push-out test results from this study were combined with other studies to propose a new stud strength prediction model. Three new beam tests were performed to study the effect of the stud position in the ribs of the steel deck. The results of these tests, along with 61 other beam tests, were used to verify the new stud strength prediction model. A reliability study was performed to determine resistance factors for stud strength and beam strength. / Ph. D.

Full-depth precast deck panels are a promising alternative to the conventional cast-in-place concrete deck. They afford reduced construction time and fewer burdens on the motoring public. In order to provide designers guidance on the design of full-depth precast slab systems with their full composite strength, the horizontal shear resistance provided at the slab-to-beam interface must be quantified through further investigation. Currently, all design equations, both in the AASHTO Specifications and the ACI code, are based upon research for cast-in-place slabs. The introduction of a grouted interface between the slab and beam can result in different shear resistances than those predicted by current equations. A total of 29 push off tests were performed to quantify peak and post-peak shear stresses at the failure interface. The different series of tests investigated the surface treatment of the bottom of the slab, the type and amount of shear connector and a viable alternative pocket detail. Based on the research performed changes to the principles of the shear friction theory as presented in the AASHTO LRFD specifications are proposed. The proposal is to break the current equation into two equation that separate coulomb friction and cohesion. Along with these changes, values for the coefficient of friction and cohesion for the precast deck panel system are proposed. / Master of Science

The objective of the research reported herein is to present a comprehensive evaluation of all available experimental data from push-out tests utilizing the ELCO Grade 8 standoff screws. The goal is to develop a strength prediction equation and determine reliability parameters compatible with the Load Factor Resistance Design (LRFD) procedure that would allow the use of this shear connector in design of composite floor systems. The study considers results from push-out tests using this type of screw reported by Hankins et al. (1994), Alander et al. (1998), Webler et al. (2000), and Mujagic et al. (2000). Further, this study identifies the limitations in earlier approaches aimed at predicting the strength of standoff screws. An improved strength prediction model is developed that considers all applicable limit states and determines maximum strength of a connector. A reliability study was also conducted to derive strength reduction factors to be used in design. Parameters considered in the model include deck type and geometry, screw height, concrete compressive strength, top chord angle yield strength, and stand-off screw rupture strength. Results from strength prediction model were compared with results from composite joist tests. / Master of Science

This study consists of three self-standing parts, each dealing with a different aspect of design of composite steel-concrete flexural members. The first part deals with a new type of shear connection in composite joists. Composite steel-concrete flexural members have increasingly become popular in design and construction of floor systems, structural frames, and bridges. A particularly popular system features composite trusses (joists) that can span large lengths and provide empty web space for installation of typical utility conduits. One of the prominent problems with respect to composite joists has been the installation of welded shear connection due to demanding welding requirements and the need for significant welding equipment at the job site. This part of the study presents a new type of shear connection developed at Virginia Tech— standoff screws. Results of experimental and analytical research are presented, as well as the development of a recommended design methodology. The second part deals with reliability of composite beams. Constant research advances in the field of composite steel-concrete beam design have resulted in numerous enhancements and changes to the American design practice, embodied in the composite construction provisions of the AISC Specification (AISC 1999). Results of a comprehensive reliability study of composite beams are presented. The study considers specification changes since the original reliability study by Galambos et al. (1976), considers a larger database of experimental data, and analyses recent proposals for changes in design of shear connection. Comparison of three different design methods is presented based on a study of 15,064 composite beam cases. A method to consider effect of degree of shear connection on strength reduction factor is proposed. Finally, while basic analysis theories between the two are similar, requirements for determining the strength of composite beams in Eurocode 4 (CEN 1992) and 1999 AISC Specification (AISC 1999) differ in many respects. This is particularly true when considering the design of shear connections. This part of the dissertation explores those differences through a comparative step-by-step discussion of major design aspects, and accompanying numerical example. Several shortcomings of 1999 AISC Specification are identified and adjustments proposed. / Ph. D.