The purpose of this study is to investigate the effect of lap joint length on structural performance under ultimate load using both nonlinear numerical analysis and laboratory experiments. Three-dimensional (3D) finite element models were employed for the numerical simulations, which were carried out using LUSAS software. A typical four-point bending system was modelled in order to analyze the impact of lap length. In total, 24 cases of lap length were studied across three concrete grades: C30, C45, and C60. The study also examined the influence of beam depth, shear link spacing, and concrete grade on lap joint performance. In order to validate the reliability of the 3D model, experimental data from RC beam test specimens were used.

In the design of reinforced concrete structures, the bond property is crucial. This is important for achieving the composite action between the two materials constituents, allowing loads to be efficiently transmitted. The higher strain hardening and ductility capacity of stainless steel over mild steel are one of its major benefits. International design codes, such as Eurocode 2, do not provide a separate design model for concrete structures with stainless reinforcing bars. The background paper to Eurocode 2 highlighted that there is no technical reason of why the Eurocode 2 design model cannot be used in conjunction with other types of reinforcement, provided allowance is made for their properties and behaviour. While this notion is valid when using a mild steel reinforcing bar, it produces erroneous results when a stainless reinforcing bar with a lap splice is used in a reinforced concrete section. Even though there has been a large number of studies on the behaviour of structure with stainless steel in recent years, most of it has been on plain stainless-steel members rather than reinforced concrete or stainless-steel reinforced concrete with lap splice. As a result, the purpose of this chapter is to evaluate and compare the behaviour of stainless and mild steel reinforced concrete with and without lap splices.

AbstractThis paper describes an experimental program, which investigates the validity of using Expression 7.21 in Eurocode 2 for calculating shrinkage curvatures of loaded reinforced concrete beams cracked in flexure, this Expression having previously been validated for use with uncracked sections but not for cracked sections. The experimental method used a heating technique, which exploited the differing coefficients of expansion of limestone concrete and stainless steel reinforcement to impose simulated shrinkage strains on a range of rectangular beams of various sizes and reinforcement percentages. The results indicate that Expression 7.21 is valid for use with sections cracked in flexure but may overestimate curvatures by significant amounts. It is shown that improved estimates of curvature are given by using Expression 7.18 in conjunction with Expression 7.21 with the best results being obtained by setting β = 0.3 or by using an adjusted value for the cracking moment (Mcr), as detailed in the paper.

The paper reports on an experimental investigation into the performance of lapped joints in structural concrete. The investigation focuses primarily on concrete covers close to or below the minimum set for structural reasons in design codes such as Eurocode 2 or ACI 318. Two other parameters are also varied in the tests reported here, namely the proportion of bars lapped at a section and the relative size of the bars within a lapped pair. It is found that a reduction in minimum cover from 1·2 to 0·6 times bar diameter would require an increase in lap length of 21% to develop the same stress in a lapped bar. It is verified that provisions for lapped joints in the fib Model Code 2010 are valid for minimum covers down to 0·5 times the diameter of a lapped bar. It is also found that lap strength does not change significantly when laps are staggered. The finding raises questions over the validity of the α6 coefficient in Eurocode 2, which is dependent on the proportion of bars lapped at a section. Results demonstrate that, where lapped bars differ in diameter, lap length may safely be based on the diameter and covers to the smaller diameter bar.