Concrete Hollow Core Slabs Research Articles

Algorithm and Program for Simulating Heat Transfer in Cavities of Structural Members under Fire Conditions

In this paper, an algorithm based on the network method suggested by Oppenheim for calculating the radiative heat flow in a cavity of structural members, say hollow core concrete slabs, exposed to fires is presented. It is assumed that the pressure in a cavity keeps atmospheric pressure through the whole cause of a fire, and the lost heat from the air due to expansion and immediate moving away from a cavity is neglected. The heat in a cavity is transfer via both heat conduction in air and thermal radiation among boundaries, and special regard is paid to modeling heat transfer by radiation. The effective radiative heat flow system of equations is derived and expressed in matrix form. The system of equations features a symmetric coefficient matrix, which can be stored in a one dimensional array, and can be solved using LDLT factorization. Node radiative thermal loads are calculated from effective radiative heat flows at edges of elements located on internal cavities. The nonlinear finite element program TFIELD written by first author has employed the new algorithm. Temperature distribution in two structural members with cavities are calculated using TFIELD, and numerical results demonstrate that the new algorithm is very effective and is useful for further study of structural behavior of structural members under fire conditions.

Different CFRP strengthening techniques for prestressed hollow core concrete slabs: Experimental study and analytical investigation

Abstract This study presents an experimental–analytical investigation on the structural behavior of precast prestressed hollow core RC slabs strengthened in flexure by CFRP laminates. Externally bonded and near surface mounted (NSM) laminates were used. The CFRP area and using transverse anchorage were also investigated. Results demonstrated that NSM technique resulted in optimum strengthening efficiency. The increased bond strength also resulted in full activation of the NSM laminates at failure. However, the NSM flexural strengthening level should be carefully designed to avoid unfavorable shear-tension failure mode. Moderate efficiency was associated with the externally bonded technique due to the premature de-bonding. However, this efficiency was optimized by using transverse CFRP laminates as anchorage, which re-directed de-bonding further away from the laminates’ ends and delayed failure, but at much lower deformations than those of the control slab. A rational analytical study was conducted. Comparisons between the experimental and analytical results demonstrated satisfactory agreements.

Hollow‐core concrete slabs exposed to fire

AbstractThe aim of this paper is to provide recommendations to designers and to propose a simple method for designers to model the structural behaviour of hollow‐core concrete (HC) floor slabs in fire. The proposed finite element model incorporates a grillage system using beam elements to capture the thermal expansion of the precast units in both directions, with the topping concrete over several precast units modelled by shell elements. The research reported herein compares the proposed model with various fire test results of HC slabs. The simulation outcomes show good agreement with the experimental results.Several HC slab flooring systems tested previously at the University of Canterbury for seismic purposes were simulated using this modelling scheme. Various supporting schemes have been considered, and the results show that different arrangements of axial and rotational restraint at the supports can significantly influence the fire performance of the concrete slab floors. Copyright © 2008 John Wiley & Sons, Ltd.

Tests and analysis on shear strength of composite slabs of hollow core units and concrete topping

Prestressed concrete hollow core slabs are commonly used as load-bearing floors and roofs. The upper surface of the hollow core slabs is usually levelled with a cast-in situ screed or concrete topping. Reducing the thickness of the precast unit and increasing the thickness of the concrete topping, but maintaining the load-carrying capacity for the whole composite section is technically and economically an interesting alternative. The expensive screed could be replaced by a cheaper concrete and installations could be embedded in the topping layer. Proper shear and bond strength at the interface is required for composite action. An experimental and theoretical study on the effect of structural topping on the shear capacity of hollow core slabs and of the adequacy of the shear or bond strength of the non-treated interface is presented. It is concluded that concrete topping can be used to improve the shear capacity of hollow core units. For the test specimens, the theoretical increase was of the order of 35%, which was verified by the tests. The bond strength at the interface is adequate and the topping interacts with the slab in a proper manner.

Short-term and long-term deflection of reinforced hollow core concrete slab systems

This paper presents a study on different methods of analysis that are currently used by design codes to predict the short-term and long-term deflection of reinforced concrete slab systems and compares the predicted deflections with measured deflections. The experimental work to measure deflections involved the testing of full-scale slabs joined together and, with toppings of different strengths, as simple supported panels. A model based on stress redistribution in concrete in tension and tensile steel reinforcement, due to cracking, was proposed and its predictions were also compared with measured deflections. For the prediction of the long-term deflection, a measured ratio of long-term deflection to short-term deflection was compared with the ACI long-term factor.Keywords: short term deflection, long-term deflection, concrete, crackingBotswana Journal of Technology Vo 14(1) 2005: 51-62

Experimental study on semi-rigid composite joints with steel beams and precast hollowcore slabs

The concept of semi-rigid composite connection has been widely researched in the past; however, most of the researches are limited to composite joints with metal deck flooring and solid concrete slabs. Composite construction incorporating precast concrete hollowcore slabs (HCU) is a recently developed composite floor system for buildings. The research on the structural behaviour of the semi-rigid composite joints with HCU is new and without any previous experimental database. In this paper, eight full-scale tests of beam-to-column semi-rigid composite joints with steel beams and precast hollowcore slabs are reported. The variables are stud spacing, degree of the shear connections, area of the longitudinal reinforcement and slab thickness. The test set-up and instrumentation is described in detail. The experimental behaviour is analysed and based on the test data the structural behaviour of these semi-rigid composite joints is discussed. Based on the experimental data, a simplified method to predict rotation and moment capacity for this type of composite connection is proposed.

Waved Joint for Seismic-Resistant Precast Floor Diaphragms

Floors made of precast concrete hollow-core slabs may be constructed without a structural concrete topping and with transverse tie reinforcement placed only out of the slabs. Longitudinal joints between adjacent precast units are filled with mortar on site. To ensure good diaphragm performance under seismic action, a special joint has been devised, in which the slab sides are profiled as continuous sinusoidal waved shear keys. The research involved experimental investigations and analytical modeling. The features of the joint and the means of production were first worked out. Then, a series of destructive tests were performed, on both short joint samples and full-scale floors, made of extruded prestressed hollow-core slabs without topping, all subjected to large in-plane loading reversals. They showed that, after the adhesion between the grout and precast concrete is overcome, a stable cyclic shear transfer mechanism develops, based on wedge action and friction raised at the wavy slab–mortar interface. Th...

Implementation of the Maturity Method for Zero-Slump Concrete Products

This paper describes the implementation of the maturity method at Prestressed System Incorporated's precast concrete hollow core plant. The objectives of the investigation were: to investigate the methods and materials used to produce precast concrete hollow core slabs; evaluate the practice of making, curing, and testing zero-slump concrete test cylinders; determine the appropriate maturity functions for zero-slump concrete; correlate the maturity method with measured compressive strength to calculate required maturity values that equate to specified hollow core concrete compressive release strengths.

空胴プレストレストコンクリート床板組立構造システムの開発 : 水平荷重に対する抵抗(構造)

The present paper discusses on the mechanical behaviors of the continuous prestressed concrete hollow core slabs with connection of coupling reinforcement and joint concrete. The mechanical behavior of continuous PC hollow core slabs was investigated by shear test using the test specimen with real scale. On the basis of the test results obtained, the evaluation formula for the shear transfer capacity is proposed for structural design.

空胴プレストレストコンクリート床板組立構造システムの開発 : 工法概要,鉛直荷重に対する抵抗(構造)

The present paper discusses on the mechanical behaviors of the continuous prestressed concrete hollow core slabs with connection of coupling reinforcement and joint concrete. The mechanical behavior of continuous PC hollow core slabs was investigated by flexural and shear test using the test specimen with real scale. From this data, it was found that the length of coupling reinforcement in the hollow core slab gave the great influence on flexural behavior and the connection capacity. And also, it was recognized that analytical results obtained from proposed design formula capacity with test data.

Designing composite steel beams with precast concrete hollow-core slabs

This paper presents a design procedure for steel beams acting compositely with proprietary precast hollow-core slabs. It also contains selected underpinning theoretical analyses that illustrate the rationale behind the design formulae and recommendations. Numerical results for the transfer of horizontal compressive forces through the numerous interfaces and through the load–slip characteristics of the shear studs are presented, i.e. the interfaces between the precast slab and in situ concrete infill, and the in situ infill and steel beam. A method for designing composite beams, including the effective breadth of the precast slab, the degree of shear interaction and prediction of the moment capacity, is given. Load against span graphs for composite beams are provided for use in initial design. A worked example based on the procedures illustrates their application in practice.

A ventilated slab thermal storage system model

A simplified dynamic thermal model of a hollow core concrete slab thermal storage system and associated room is described. The model is based on a thermal network that can address the heat exchange between the slab cores and the ventilation air, the thermal storage in the building fabric, and the effect of the heat disturbances on the room. The increase in convective heat transfer at the corners of the ventilation cores is also discussed. For normal cyclic operation, the simulated mass and zone temperatures are both in phase with measured performance data. The model root mean square error between the simulated and measured performance is no more than 0.5 °C for the average slab mass temperature and 1.0 °C for the zone air temperature.

Reliability-Based Optimization of Plant Precast Concrete Structures

This paper presents a decision model for minimizing the life-cycle cost of prefabricated concrete elements and structures, taking into account the building design-manufacturing-construction-service life process as a whole. The decision model utilizes principles of engineering economic analysis under uncertainty in considering costs and benefits of construction, maintenance, repair, and consequences of failure. The concepts are illustrated for plant precast hollow-core concrete floor slabs. Decision variables can include parameters related to concrete quality, manufacturing process technology, and maintenance. The optimal solution identifies those values of the decision variables that result in minimum expected total cost. The performance constraints, in the form of limits on the probability of flexural failure, shear failure, cracking, and excessive deflection are formulated using principles of structural reliability theory.

Design for Vertical Load on Horizontal Connections in Large Panel Structures

T Ire essential difference between a cast-in-place concrete structure and a precast large panel structure is the nature of connections between elements. Connections serve to transfer forces between elements. The ability of large panel structures to perform satisfactorily under all loading conditions depends on the integrity of the connections. Connections must transmit gravity loads from floor to wall elements, from wall to wall elements, and from wall elements to the foundation. If connections are inadequate, the design strength of the adjoining elements may not be fully utilized. However, the design strength of walls may be considerably greater than the required strength. Connections are classified' with respect to location, direction, and funetion. They may be interior or exterior, horizontal or vertical, and wall-to-wall or wall-to-floor connections. A wall-tofloor connection is known also as a horizontal joint or a horizontal connection. The most widely used horizontal connection is the platform connection, also known as the closed or American type connection. The interior American connection as shown in Fig. 1(a) consists of precast top and bottom wall panels, and prestressed concrete hollow-core slabs supported continuously on plastic bearing pads. The space between the ends of floor planks is filled with castin-place grout which may also fill a part of the hollow slab cores. The wall panel above the connection rests on drypacked mortar approximately 1-in. (25 mm) thick, Mortar is packed from both sides of the wall to completely fill the

LOAD DISTRIBUTION TEST ON PRECAST HOLLOW CORE SLABS WITH OPENINGS

In many applications of prestressed concrete hollow-core slabs as floor systems, it is necessary to provide large openings through some units for mechanical and plumbing requirements. Openings through an individual unit may require removal of as much as 50 percent of the cross section. In most cases, this design can be accomplished by transferring the load to adjacent full units. (1), (2) This investigation covers a load test which was conducted to assist in verifying such a design approach. A floor system of 6 in. thick hollow-core units with a 40 x 40-in, cutout was used for the test (see Fig. 1). In the investigation the following points were of interest: 1. What is the capacity of the system? 2. How effective is the shear key in transferring load? 3. What type of local cracks result before failure? 4. What type of failure results at ultimate load?