Design of plate-reinforced composite coupling beams for tall buildings

Plate-reinforced composite (PRC) coupling beams are fabricated by embedding a vertical steel plate into conventional reinforced concrete coupling beams to enhance their strength and deformability. Shear studs are weld on the surfaces of the steel plate to transfer forces between the concrete and steel plate. Based on extensive experimental studies and numerical simulation of PRC coupling beams, a design procedure based on Hong Kong design codes of practice is proposed to aid engineers in designing this new type of beams. The proposed design guidelines consist of four main parts, which are (1) estimation of ultimate shear capacity of beam, (2) design of RC component and steel plate, (3) shear stud arrangement in beam span, and (4) design of plate anchorage in wall piers. An example is given to illustrate the use of the guidelines for the design of PRC coupling beams.published_or_final_versionSymposium on Contemporary Seismic Engineering 2010, Hong Kong, 27 August 2010. in Proceedings of the Symposium, 2010, p. 63-8

Three-dimensional mixed mode analysis of a cracked body by fractal finite element method

A semi-analytical method namely fractal finite element method is presented for the determination of stress intensity factor for the straight three-dimenisonal plane crack. Using the concept of fractal geometry, infinite many of finite elements are generated virtually around the crack border. Based on the analytical global displacement function, numerous DOFs are transformed to a small set of generalised coordinates in an expeditious way. No post-processing and special finite elements are required to develop for extracting the stress intensity factors. Examples are given to illustrate the accuracy and efficiency of the present method. Very good accuracy (with less than 3% errors) is obtained for the maximum value of SIFs for different modes.postprin

Plate-strengthened deep reinforced concrete coupling beams

Many old reinforced concrete buildings in developed countries need to be strengthened due to the aging of construction materials, changes in functional use or new design loading requirements. In the present study, a series of experiments were conducted attempting to retrofit deep reinforced concrete coupling beams using a bolted steel plate. In addition to the control specimen, the other specimens were bolted with a steel plate on the side face to improve the shear strength and inelastic behaviour. A mechanical device was added to two specimens to restrain plate buckling. The study revealed that adding an external plate is an effective way to improve the shear capacity, energy dissipation and rotation deformability of deep reinforced concrete coupling beams. Moreover, the plate buckling-restrained specimen with a sufficient number of bolts in the anchor regions had a more stable response and better inelastic performance under reversed cyclic loads. These findings can help designers to a better understanding of this type of composite coupling beam.published_or_final_versio

A double-cylinder model incorporating confinement effects for the analysis of corrosion-caused cover cracking in reinforced concrete structures

In this paper, a double-cylinder model with a consideration of concrete confinement effects is proposed to simulate reinforcement corrosion-caused cover cracking. The analytical model incorporates force equilibrium in both tangential and radial directions as well as volume expansion and deformation compatibility in the steel-rust-concrete interface. Confinement effects outside the cylinders are taken into account by comparing the numerical and available experimental results. Parametric studies are conducted to investigate the variations of the critical volume of consumed steel, critical expansive pressure and time to cover cracking.postprin

Numerical solution of cracked thin plates subjected to bending, twisting and shear loads

A semi-analytical method namely fractal finite element method is presented for the determination of mode I and mode II moment intensity factors for thin plate with crack using Kirchhoff's theory. Using the concept of fractal geometry, infinite many of finite elements is generated virtually around the crack border. Based on the analytical global displacement function, numerous degrees of freedom (DOF) are transformed to a small set of generalised coordinates in an expeditious way. The stress intensity factors can be obtained directly from the generalized coordinates. No post-processing and special finite elements are required to develop for extracting the stress intensity factors. Examples of cracked plate subjected to bending, twisting and shear loads are given to illustrate the accuracy and efficiency of the present method. The influence of finite boundaries on the calculation of the moment intensity factors is studied in details. Very accuracy results when compare with the theoretical and numerical counterparts are found.postprin

Gravity-induced shear force in reinforced concrete walls above transfer structures

In this study, the gravity loads in reinforced concrete shear walls supported on transfer structures are investigated. Emphasis is placed on the shear-stress concentration effects on the supported shear walls owing to the distortion of the transfer structure. A simplified model is proposed to illustrate the fundamental physical interactions. Finite-element analysis is also conducted to study the influences of the symmetric and asymmetric shear-wall arrangements, positioning of supporting columns and span-to-depth ratio of the transfer structure. Non-linear behaviours encompassing the use of yielded stiffness at ultimate limit state, sequential construction and the creep of reinforced concrete under gravity loads are addressed. Various effects of modelling assumptions and simplifications on the stress redistribution of the transfer structure are investigated. Remedial measures are proposed, such as increasing the depth of the transfer girders using late-cast slabs, segmented upper shear walls and concrete of higher grade for critical regions.published_or_final_versio

Experimental study on fracture behavior of pre-notched mortar beams using ESPI technique

Electronic Speckle Pattern Interferometry (ESPI) technique is of high sensitivity and can provide full-field surface deformation. This paper introduces the application of ESPI technique to measure the surface deformation of pre-notched mortar beams in three-point bending tests. In addition to ESPI, Linear Variable Differential Transformers (LVDTs) and clip gauge extensometer were used to measure the mid-span deflection and Crack Mouth Opening Displacement (CMOD) of the beam respectively. Displacements measured by ESPI are compared with that obtained from LVDTs and clip gauge to verify the accuracy of ESPI. From the displacement field measured by ESPI, one of the nonlinear fracture properties of quasi-brittle materials, Crack Tip Opening Displacement (CTOD) was determined and load-CTOD curve is plotted. Furthermore, crack propagation process and Crack Opening Displacement (COD) profiles at different loading stages are presented. Some fracture parameters of the mortar specimen are quantified.postprin

Experimental and numerical studies of external steel plate strengthened reinforced concrete coupling beams

This paper aims to develop a new method for strengthening reinforced concrete (RC) coupling beams. Experiments were conducted to test three full-scale RC coupling beams, of which two were strengthened by bolted external steel plates on the side faces of the beams and the other one acted as a control specimen without strengthening. The improvements to strength, deformation and energy dissipation of the external plate strengthened RC coupling beams were observed from the experimental results. Nonlinear finite element analysis was carried out to model the strengthened and non-strengthened coupling beams. The material properties used for concrete and reinforcement in the numerical analysis were validated by the laboratory tests. As the experimental study showed that there was a small slip between the bolted connection and the concrete wall pier, a bilinear model was used to simulate the load-slip behaviour of the bolt connections. The model was calibrated by the experimental results from the plate strengthened coupling beams. A numerical parametric study found that the small slip (>3 mm) between the bolt connection and the concrete wall could significantly affect the load-carrying capacity of the bolt connections as well as the structural performance of the strengthened coupling beams. The numerical model developed is very useful for investigating strengthened beams with other configurations and other reinforcement details. © 2005 Elsevier Ltd. All rights reserved.postprin

Mixed mode cracks in Reissner plates

Based on the sixth order Reissner plate theory, the generalized displacement functions for a cracked plate are derived by eigenfunction expansion method. The fractal two-level finite element method is employed to obtain the stress (moment and shear) intensity factors for the center cracked plate subjected to out-of-plane bending and twisting loads. The numerical results from the present method are checked with those available in literature. Highly accurate stress intensity factors are predicted for a wide range of thickness to crack length ratio and a full range of PoissonÆs ratio provided that the radius of fractal mesh to thickness ratio is not less than 1/10.postprin

Accurate determination of mode I and II leading coefficients of the Williams expansion by finite element analysis

Leading coefficients of the Williams expansion are evaluated by using the fractal finite-element method (FFEM). By means of the self-similarity principle, an infinite number of elements is generated at the vicinity of the crack tip to model the crack tip singularity. The Williams expansion series with higher-degree coefficients is used to capture the singular and non-singular stress behaviour around the crack tip and to condense the large amount of nodal displacements at the crack tip to a small set of unknown coefficients. New sets of coefficients up to the sixth degree for mode I and fourth degree for mode II problems are solved. The important fracture parameters such as stress intensity factors and T-stress can be obtained directly from the coefficients without employing any path independent integrals. Convergence study reveals that the present method is simple and very coarse finite element meshes with 12 leading terms in the William expansion can yield very accurate solutions. The effects of the influence of crack length on the higher-degree coefficients of some common plane crack problems are studied in detail. © 2005 Elsevier B.V. All rights reserved.postprin