Foamed concrete is produced when a foaming agent IS added to cement-based slurry consisting of cement, water, cement extender and filler. This lightweight building material can contribute significantly to uplift disadvantaged communities when used during the development of infrastructure. To achieve this goal, in depth research into the structural properties of the material is essential. Since 1992 tests to determine structural properties of foamed concrete have been conducted at the University of Pretoria. The results show that the compressive strength of foamed concrete is a function of age, ash/cement ratio and porosity and for a given porosity and age there is an optimum ash content, resulting in the maximum compressive strength. The focus of this research is therefore on foamed concrete mixtures with target densities varying between 700 kg/m3 and 1500 kg/m3 where the question that needed to be answered is: what is the influence of the microstructure on the physical and structural properties of these mixtures? The study is restricted to the effect of the microstructure on the relation between the physical properties (such as density, ash/cement ratio and porosity), and the structural property (compressive strength) of foamed concrete. In order to evaluate the influence of the microstructure on these relationships it was necessary to develop parameters to explain and quantify the microstructure of foamed concrete. An image processing and analysis system was applied to develop the air-void size distribution parameters and the air-void spacing parameters. These parameters were used to represent the microstructure (entrained air-void structure) of the foamed concrete mixtures. It was therefore now possible to plot graphs showing the effect of the microstructure on the physical and structural properties of foamed concrete. It was established that the 28-day dry densities have an influence on the air-void size distribution. In turn the air-void size distribution has an influence on the average % porosities and 28-day compressive strength of foamed concrete. The 28-day dry densities have no influence on the spacing of air-voids and in turn the spacing of the air-voids does not have any influence on the average % porosity and 28-day compressive strength. / Dissertation (M Eng ( Structural Engineering))--University of Pretoria, 2007. / Civil Engineering / unrestricted

The optimum design, with respect to cost, of reinforced concrete structures, satisfying Building Code Requirements (ACI 318-63), is investigated, using Box's Complex Method. Variables considered are: geometry, topology, member sizes and material properties. The optimum design, with respect to volume of single span, pin-connected, plane trusses, is investigated, using Box's Complex Method. Variables considered are: member sizes and nodal co-ordinates. The feasibility of the Complex Method is probed by checking the results, either by conducting exhaustive search or comparing them with solutions obtained with linear programming methods. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The investigation dealt mainly with the shear transfer capacity of a joint between a precast concrete column and a cast-in-place concrete beam. Four reinforced concrete frames, each consisting of two columns and two beams, were cast, assembled and tested in a special loading frame. To obtain a general pattern of failure mechanisms, a series of loads consisting of different ratios of moments, shears and axial forces were imposed on these frames. All recording of test data was done electronically in the form of punched tape to facilitate computer analysis. The investigation showed clearly that high values of shear transfer can be reached even under the most adverse load conditions. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Inelastic behavior is inevitable in most structures subjected to strong earthquake forces. Any rational design procedure, therefore, should attempt to estimate the amount of inelastic behavior to be expected in each member of the structure. Methods of dynamic response analysis based on linear elastic assumptions can be carried out conveniently and economically. Such methods, however, can not provide any direct information on the inelastic behavior of the structure. On the other hand, time-step analysis programs can 'truly' simulate the non-linear behavior of the structure but are seldom used because of their cost and complexity. There is, therefore, a need for practical and efficient methods which can account for the inelastic behavior. Some methods for estimating the inelastic response and damage patterns of structures under ground motions are presented. One is the Modified Substitute Structure Method which is now revised so that the structure can be analysed for gravity loads prior to the seismic analysis. The other method which is proposed here uses a static analysis. The structure is first analysed for gravity loads and then lateral seismic forces (as given by the appropriate codes) are applied. The amplitude of the lateral forces is gradually increased, maintaining the specified pattern; a plastic hinge is placed where a member has yielded and the structure stiffness matrix revised each time. This process is continued until the structure has reached a predetermined displacement. At this point, the rotation of the plastic hinges is known and then the member curvature ductilities can be calculated. Thus, an idea is obtained, of the damage pattern in the structure. A computer program has also been written for analysing the structures by 'Freeman's Method' to predict the inelastic response of structures under severe ground motion. The method gives the overall inelastic response without predicting the pattern of local damage. These various methods are then compared by analyzing two idealized structures. A third, real structure, an office/residential building in downtown Vancouver is also analysed by these methods and the results compared with those obtained by a time-step analysis program DRAIN-2D. These methods appear to give good results and it is hoped that they will be found useful by practising engineers. A user's guide and the listing of these programs are included in the appendices. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Under seismic excitation, the centre of stiffness of an eccentric structure is stationary as long as the structure remains elastic. Once yielding occurs, the centre of stiffness will begin to move away from its original position, as the torsional forces induced by the eccentricity cause uneven distribution of yielding among members. This movement of the centre of stiffness very often increases the eccentricity of the structure causing further damage. The purpose of this thesis is to determine the significance of this magnification of the initial eccentricity. A procedure for locating the centre of stiffness was developed and incorporated into a time-step dynamic analysis program code named DRAINTABS. Two models were chosen to describe the moment-rotation relationship of reinforced concrete members; the elasto-plastic model and the Takeda model. The former is a bilinear model whereas the latter takes into account the strength degradation of reinforced concrete members under cyclic loading. A number of reinforced concrete buildings were studied. It was found that the centre of stiffness did not always move towards the side of the structure which was more heavily loaded due to the torque induced by the eccenticity. Excursions in the other direction were possible when the translational motion was not in phase with the torsional motion at the instant of maximum excursion. Moreover, when the strength degrading characteristic of R/C members was modelled, the eccentricity of the structure increased gradually with increasing length of excitation. However, this increase was found to be small and therefore insignificant. The procedure for locating the centre of stiffness was also incorporated into another analysis program code named PITSA which utilizes the modified substitute structure method. The results obtained were compared to those obtained using DRAINTABS. Although PITSA has been proven to be a relatively inexpensive yet reliable alternative to a time step analysis, it failed to predict the maximum displacement of the centre of stiffness with any acceptable degree of accuracy. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The research on headed stud connections described in this dissertation forms a part of an overall objective of predicting the behaviour of precast concrete panel buildings under earthquake loads. Existing laboratory test data and current design procedures of headed stud connections are briefly reviewed. It is postulated that shear loads are transmitted via a connection to the surrounding concrete by three distinct mechanisms: 1. friction between faceplate and concrete 2. bearing of end of faceplate on concrete 3. interaction between studs and concrete Tests on laboratory models designed to isolate individual aspects of these mechanisms confirm that all three exist. Friction forces between faceplate and concrete are small in comparison with the remaining forces acting in a connection, particularly under cycled loading. Bearing of the end of the faceplate on concrete and interaction between studs and surrounding concrete are shown to be the main contributions to the total load carried by a connection. A simple analytical model is presented for the prediction of the ultimate shear load capacity of a connection and a computer algorithm is proposed for the prediction of the load versus deflection behaviour of a connection under both monotonic and cyclic conditions. Existence of the three mechanisms whereby a connection transfers applied shear forces to the surrounding concrete contradicts the shear friction equation which is currently used in the design of connections. The analytical equations developed in the investigation indicate that the strength of a connection is directly dependent upon the strength of the surrounding concrete, as opposed to the expression for shear friction, which does not contain concrete strength as a variable. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

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