591 research outputs found

    Recent research and development in semi-rigid composite joints with precast hollowcore slabs

    Get PDF
    Composite structure incorporating steel beams and precast hollowcore slabs is a recently developed composite floor system for building structures. This form of composite construction is so far limited to simple beam-column connections. Although the concept of semi-rigid composite joints has been widely research in the past, most of the researches have been carried out on composite joints with metal deck flooring and solid concrete slabs. Research on composite joints with precast hollowcore slabs is rather limited. As the construction industry demands for rapid construction with reduction in cost and environmental impacts, this form of composite floor system, which does not require major onsite concreting, has become very popular among the designers and engineers in the UK. In this paper, full-scale tests of beam-to-column semi-rigid composite joints with steel beam and precast hollowcore slabs are reported. Based on the tests data; the structural behaviour of these semi-rigid composite joints is discussed together with numerical and finite element modelling. Through parametric studies, an analytical model for the semirigid composite joints is proposed and is verified by both the experimental data and finite element model; and good agreement is obtained

    Finite element modeling of the composite action between hollowcore slabs and the topping concrete

    Get PDF
    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 Modeling of the Interface between Lightly Roughened Hollowcore Slabs and Cast-In-Place Concrete Topping

    Get PDF
    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

    STR-885: FINITE ELEMENT MODELLING OF COMPOSITE HOLLOWCORE SLABS

    Get PDF
    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

    Effect of aspect ratio on fire resistance of hollow core concrete floors

    Get PDF
    Previous studies have shown that the fire performance of hollowcore units is significantly affected by the end support conditions, but it has not been clear how the fire resistance of the overall floor system can be improved by providing side supports. The previous studies used beam grillage and shell elements to separately model the hollowcore units and the topping concrete slab using the platform of the non-linear finite element program SAFIR. The modelling method required a lot of computational resources and is not ideal to model a large floor area. This paper describes the effect of the side supports and the aspect ratio of the floor on the predicted fire resistance. It also compares the efficiencies of shell elements and short beam elements for finite element modelling of the topping concrete in fire conditions. The results show that integrating the topping concrete slab into the beam grillages reduces the complexity of the model and also provides satisfactory results. Side supports can increase the fire performance of hollowcore floor slabs provided that the spacing of the side supports does not greatly exceed the span length

    Shear and Peel Stresses at the Interface between Hollowcore Slabs and the Topping Concrete

    Get PDF
    Hollowcore slabs are used in floors and roofs of residential, commercial, industrial and institutional buildings. They are precast/prestressed concrete elements produced using the extrusion process. Their surface finish can be “machine-cast” or “intentionally roughened”. A typical floor consists of a number of hollowcore slabs that are connected together. Prestressing causes hollowcore slabs to camber, which results in an uneven floor surface. A 50 mm topping concrete is commonly cast to level the floor surface. To avoid delamination, engineers require bonding agents to be applied on the hollowcore slab surface before pouring the topping concrete. The concrete topping can be used compositely with the hollowcore slabs to increase the floor’s load carrying capacity. However, North American design standards require intentional roughening of the hollowcore slab surface to consider such composite action. This requirement results in added cost that manufacturers are keen to avoid. This thesis presents a comprehensive experimental program to assess the performance of composite hollowcore slabs with machine-cast and lightly-roughened surface finishes. Three types of tests were performed: pull-off, push-off and full-scale. They provided an overall understanding of the interfacial shear and peel behaviors at the interface between hollowcore slabs and the topping concrete. The tested slabs were found to sustain higher interfacial shear stresses than the limits set by the design standards and to provide adequate composite behavior up to failure. Linear analytical modeling in which closed-form solutions for differential equations governing the interfacial shear and peel stresses during the push-off tests was conducted. Two analytical methods were developed to estimate the shear and peel stresses during the full-scale tests utilizing the interface stiffness determined from the pushoff tests. Linear finite element analysis was performed to validate and compare the proposed methods. To better understand the experimental results and to provide engineers with more accurate tools for estimating the interfacial stresses, nonlinear finite element analysis of the push-off and the full-scale tests were conducted. Interfacial shear and peel stiffness values associated with the tested slabs were also determined to assist design engineers in predicting failure modes of composite hollowcore slab

    Experimental Investigation of the Composite Action between Hollowcore Slabs with Machine Cast Finish and Concrete Topping

    Get PDF
    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

    Implementing environmental improvements in a manufacturing context: a structured approach for the precast concrete industry

    Get PDF
    In common with other industries, most of the measures and solutions employed by companies in the £2 billion UK precast concrete manufacturing sector are linked to profitability. The concept of sustainability adds new dimensions as social progress and environmental protection become end goals in themselves, rather than objectives to achieve economic growth. This paper explores the nature of the precast industry and discusses opportunities and challenges relating to environmental improvement. A holistic view of the manufacture and procurement of precast concrete products is used to offer environmental improvement criteria an enhanced status in relation to the profitability imperative
    corecore