The ultimate strength of hollowcore slabs is greatly affected by their post-cracking behaviour. The composite action between the concrete topping and the hollowcore slab adds another level of nonlinearity. This paper presents a comprehensive finite element study to evaluate the nonlinear properties of the interface between a hollowcore slab and its concrete topping. The presented finite element modeling procedure was validated using data from a previous comprehensive experimental study by the authors. The nonlinear material behaviour of the concrete and the prestressing strands were also accounted for. The paper presents a modeling method that realistically simulates the staged construction technique of composite hollowcore slabs. Finite element results allowed understanding changes to the interface properties due to the confining effect of the applied load as well as the interaction between the shear and peel stresses.

Analytical evaluation of the interfacial shear stresses for composite hollowcore slabs with concrete topping is rare in the literature. Adawi et al. (2014) estimated the interfacial shear stiffness coefficient (ks) that governs the behavior of the interface between hollowcore slabs and the concrete topping using push-off tests. This parameter is utilized in this paper to provide closed form solutions for the differential equations governing the behavior of simply supported composite hollowcore slabs. An analytical solution based on the deformation compatibility of the composite section and elastic beam theory, is developed to evaluate the shear stresses along the interface. Linear finite element modeling of the full-scale tests presented in Adawi et al. (2015) is also conducted to validate the developed analytical solution. The proposed analytical solution was found to be adequate in estimating the magnitude of horizontal shear stress in the studied composite hollowcore slabs.

Hollowcore slabs are precast/prestressed concrete elements produced at a manufacturing plant before shipping to the job site. Following installation, a layer of concrete topping is usually cast to connect the slabs and to have a level surface. According to current North American design standards, the topping should not be considered to act compositely with the slabs except if their surface satisfies a strict roughness requirement. This paper evaluates if such restriction is justified for hollowcore slabs with machine-cast finish through an experimental program that involves pull-off, push-off and full-scale tests. The surface roughness was first evaluated. The peel (bond) and shear strengths of the interface between the slabs and the topping were then assessed using pull-off and push-off tests. Full-scale tests examined the overall behavior of the composite slabs. The tested composite slabs exhibited higher tensile and shear stresses than the limits set by North American design standards. Surface roughness threshold for machine-cast hollowcore slabs is estimated. The paper presents the initial evidence that hollowcore slabs with machine-cast surface can be considered to act compositely with the concrete topping.

Hollowcore slabs are commonly used in different types of structures. They are usually topped with a 50 mm concrete topping. Structural engineers can use this topping to increase the slab load carrying capacity. North American design standards relate the horizontal shear strength at the interface between hollowcore slabs and the concrete topping to the slab surface roughness. This paper presents results of four push-off tests on hollowcore slabs supplied by two manufacturers and roughened using a conventional steel broom. The tested slabs sustained higher horizontal shear stresses than those specified by the design standards. Utilizing the data from the push-off tests, an analytical model was applied to evaluate the shear and peel stiffnesses, ks and kp, of the interface between hollowcore slabs and concrete topping. Structural engineers can utilize ks and kp values to model the composite action between hollowcore slabs from the two manufacturers and concrete topping. The analytical model was also used to evaluate the actual distribution of shear and peel stresses.

Hollowcore slabs are commonly used for floor and roofs of residential and commercial buildings. Concrete topping, which is commonly cast for leveling purposes, can also be used to increase the load capacity of hollowcore slabs. The post-cracking behaviour of hollowcore slabs greatly affects their ultimate strength. The composite action adds another level of nonlinearity. This paper presents a comprehensive 3-D finite element model that can predict the behaviour of such composite slabs. Nonlinear springs were used to model the interface layer. The nonlinear material behaviour of the concrete and the prestressing strands were also accounted for. Innovative analysis technique to simulate the staged construction of composite hollowcore slabs is also presented. The proposed analysis is validated using results from a previous experimental study by the authors.

According to current design standards, composite action between cast-in-situ concrete topping and hollowcore slabs cannot be considered for slabs with machine cast surface finish. This paper experimentally evaluates if such restriction is justified. The surface roughness of hollowcore slabs with machine cast finish is evaluated prior to casting the concrete topping. The bond and the horizontal shear stresses that can be resisted at the interface between the hollowcore slabs and the concrete topping were then assessed using pull-off and push-off tests. A full-scale test examined the overall behaviour of the composite system. Results provide initial evidence that hollowcore slabs with machine cast surface finish act compositely with the concrete topping.

Analysis of continuous jacketed Reinforced Concrete (RC) beams requires accounting for the nonlinear behavior of the interface and the materials as well as redistribution of moments. This kind of analysis is complex and require an advanced level of knowledge and experience to perform. Engineers need simplified yet robust tools to practically predict the actual behavior of jacketed RC beams. In the current practice, slip is neglected in the analysis and monolithic behavior is assumed for the jacketed section, which result in higher estimates of stiffness and/or capacity. This paper provides a simplified method to analyze continuous jacketed RC beams taking into account the interfacial slip distribution and the actual nonlinear behavior of both concrete and steel. An iterative calculation algorithm is developed to determine the moment–curvature curves of a jacketed beam at different sections. The developed method allows the evaluation of interfacial slip and shear stress distributions in ductile reinforced concrete beams. The developed method is utilized to conduct an extensive parametric study, which resulted into modification factors that can be used to calculate the capacity and deformations of a strengthened beam considering the interfacial slip.

Analysis of jacketed Reinforced Concrete (RC) beams considering the interfacial slip effect is a complicated problem. In the current practice, slip is neglected in the analysis and monolithic behavior is assumed in the jacketed section resulting in higher estimates of stiffness and/or capacity. Engineers need simplified yet robust tools to predict the actual behavior of jacketed RC beams. This paper provides a simplified method to analyze jacketed RC beams taking into account the interfacial slip distribution and the actual nonlinear behavior of both concrete and steel. An iterative calculation algorithm is developed to determine the moment-curvature and load-deflection curves of the jacketed beams. The developed method provides an evaluation of the slip and shear stress distributions, which allow assessing the influence of surface roughness conditions. The developed method is utilized to conduct an extensive parametric study, which resulted into modification factors to calculate the capacity and deformations of strengthened beams while accounting for interfacial slip.

The necessity to rehabilitate a Reinforced Concrete (RC) structure emerges from several reasons such as new safety requirements, change of structure occupancy, incorrect design calculations and/or degradation of materials with time. One of the most commonly used mitigation practices to strengthen and repair RC beams is the application of RC jackets at either one side or three sides of the beams. The use of these jackets to improve the flexural performance of RC beams is investigated in this study. An iterative incremental algorithm that takes into account the influence of slip along the interface between the old and new concrete layers is developed. In addition, the distribution of interfacial strain gradient, slip and shear stresses along the interface are predicted. A very good agreement is shown between the current proposed analytical model and the published experimental data on RC jacketed beams. Based on an extensive parametric study, effective flexural modification factors of these beams are developed and verified.

The importance to rehabilitate ageing and deteriorated existing steel structures has motivated researchers to develop simple and efficient rehabilitation techniques. One of the currently developed techniques involves bonding Fibre Reinforced Plastic (FRP) sheets to the flanges of steel beams. This paper presents an analytical model to predict the linear and nonlinear behaviour of steel beams rehabilitated using this technique. The model is based on the solution of the differential equations governing the composite behaviour of a rehabilitated steel beam and includes representation of the peel and shear behaviour of the adhesive material. A bending test was conducted on a W-shaped steel beam, with glass FRP sheets bonded to its flanges, and the experimental results were used to validate the model. The model predictions for the failure load, failure mechanism, midspan deflection, steel strains, and FRP strains were found to be in excellent agreement with the experimental results. The model was also used to predict some parameters that were difficult to evaluate experimentally. This provided a better understanding of the behaviour of the rehabilitated beam.

The current study is a part of an extensive research program conducted to assess the use of Glass Fibre Reinforced Plastic (GFRP) sheets in enhancing the flexural capacity of steel beams. The properties of a heavy-duty adhesive system that can be used to bond GFRP sheets to the flanges of steel beams were experimentally determined in a previous study. The excellent performance of a W-shaped steel beam strengthened using GFRP sheets has encouraged the authors to assess the applicability of this technique to composite steel bridges. The dimensions and cross section properties of a real composite steel plate girder bridge are considered in a case study analysis. A detailed nonlinear numerical model is developed for the bridge before and after attaching GFRP sheets to the bottom flange of its steel girders. Nonlinear moving load analyses are first conducted to determine the critical truck locations that will lead to maximum GFRP axial stresses, and maximum adhesive shear and peel stresses. Using these configurations, nonlinear analyses are then conducted to assess the increase in the bridge capacity that can be achieved by bonding 38 mm GFRP sheet to the bottom flange of its steel girders.

Aging and deterioration of existing steel structures necessitate the development of simple and efficient rehabilitation techniques. The current study investigates a methodology to enhance the flexural capacity of steel beams by bonding Glass Fibre Reinforced Plastic (GFRP) sheets to their flanges. A heavy duty adhesive, tested in a previous study is used to bond the steel and the GFRP sheet. In addition to its ease of application, the GFRP sheet provides a protective layer that prevents future corrosion of the steel section. The study reports the results of bending tests conducted on a W-shaped steel beam before and after rehabilitation using GFRP sheets. Enhancement in the moment capacity of the beam due to bonding GFRP sheet is determined from the test results. A closed form analytical model that can predict the yield moment as well as the stresses induced in the adhesive and the GFRP sheets of rehabilitated steel beam is developed. A detailed finite element analysis for the tested specimens is also conducted in this paper. The steel web and flanges as well as the GFRP sheets are simulated using three-dimensional brick elements. The shear and peel stiffness of the adhesive are modeled as equivalent linear spring systems. The analytical and experimental results indicate that a significant enhancement in the ultimate capacity of the steel beam is achieved using the proposed technique. The finite element analysis is employed to describe in detail the profile of stresses and strains that develop in the rehabilitated steel beam.