There are many calculation methods for layered structures in scientific literature, but in most cases these calculation methods are complicated and inapplicable for layered structures made of reinforced concrete. Moreover, most of the calculation methods do not estimate the possibility of appearance of the cracks in the internal layers before the cracks in external layer in which the tensile stresses are higher. The internal layers could be made of lightweight concrete type materials (e.g. foamed concrete) which shrinkage deformations are several times higher if compared to the external layers. Therefore, the cracks in the internal layer may appear even before actual loading of the structure. The flexural layered members may have very complex state of stress and strain. Such state of stress and strain should be estimated when designing the effective and reliable building structures. The proposed method for the calculation of carrying capacity and cracking moment of the external layer of flexural layered reinforced concrete structures estimates the cracking of the internal layer, concrete shrinkage deformations and the physical and mechanical properties of used materials.

There are many calculation methods for layered structures in scientific literature, but in most cases these calculation methods are complicated and inapplicable for layered structures made of reinforced concrete. Moreover, most of the calculation methods do not estimate the possibility of appearance of the cracks in the internal layers before the cracks in external layer in which the tensile stresses are higher. The internal layers could be made of lightweight concrete type materials (e.g. foamed concrete) which shrinkage deformations are several times higher if compared to the external layers. Therefore, the cracks in the internal layer may appear even before actual loading of the structure. The flexural layered members may have very complex state of stress and strain. Such state of stress and strain should be estimated when designing the effective and reliable building structures. The proposed method for the calculation of carrying capacity and cracking moment of the external layer of flexural layered reinforced concrete structures estimates the cracking of the internal layer, concrete shrinkage deformations and the physical and mechanical properties of used materials.

The research objective was to develop a new competitively priced, high strength macrosynthetic fiber for concrete reinforcement. Mechanical bond properties were examined through aligned and inclined pullout testing. Variables involved in optimizing these properties included materials, fiber cross section, and other changes made through manufacturing processes. In addition to extensive pullout testing, improvements to fiber properties were explored through tensile testing, creep testing, and fiber performance in concrete mixtures. Practical considerations were also made, such as manufacturing processes, cost, and workability. Properties of synthetic microfibers were also considered for use in engineered cementitious composites. Synthetic macrofibers containing PVDF demonstrated high bond strength in pullout testing. Fibers demonstrating the highest performance in FRC testing were those with additional mechanical anchorage such as fibrillation or embossment. EVA as an additive did not exhibit increased interfacial bond, but further research was recommended. Further research on deformed fibers containing PVDF was also recommended.

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Reinforced concrete structures designed in pre-1970s are vulnerable under earthquakes due to lack of seismic detailing to provide adequate ductility. Typical deficiencies of pre-1970s reinforced concrete structures are (a) use of plain bars as longitudinal reinforcement, (b) inadequate anchorage of beam longitudinal reinforcement in the column (particularly exterior column), (c) lack of joint transverse reinforcement if any, (d) lapped splices located just above joint, and (e) low concrete strength. Furthermore, the use of infill walls is a controversial issue because it can help to provide additional stiffness to the structure on the positive side and on the negative side it can increase the possibility of soft-storey mechanisms if it is distributed irregularly. Experimental research to investigate the possible seismic behaviour of pre-1970s reinforced concrete structures have been carried out in the past. However, there is still an absence of experimental tests on the 3-D response of existing beam-column joints under bi-directional cyclic loading, such as corner joints. As part of the research work herein presented, a series of experimental tests on beam-column subassemblies with typical detailing of pre-1970s buildings has been carried out to investigate the behaviour of existing reinforced concrete structures. Six two-third scale plane frame exterior beam-column joint subassemblies were constructed and tested under quasi-static cyclic loading in the Structural Laboratory of the University of Canterbury. The reinforcement detailing and beam dimension were varied to investigate their effect on the seismic behaviour. Four specimens were conventional deep beam-column joint, with two of them using deformed longitudinal bars and beam bars bent in to the joint and the two others using plain round longitudinal bars and beam bars with end hooks. The other two specimens were shallow beam-column joint, one with deformed longitudinal bars and beam bars bent in to the joint, the other with plain round longitudinal bars and beam bars with end hooks. All units had one transverse reinforcement in the joint. The results of the experimental tests indicated that conventional exterior beam-column joint with typical detailing of pre-1970s building would experience serious diagonal tension cracking in the joint panel under earthquake. The use of plain round bars with end hooks for beam longitudinal reinforcement results in more severe damage in the joint core when compared to the use of deformed bars for beam longitudinal reinforcement bent in to the joint, due to the combination of bar slips and concrete crushing. One interesting outcome is that the use of shallow beam in the exterior beam-column joint could avoid the joint cracking due to the beam size although the strength provided lower when compared with the use of deep beam with equal moment capacity. Therefore, taking into account the low strength and stiffness, shallow beam can be reintroduced as an alternative solution in design process. In addition, the presence of single transverse reinforcement in the joint core can provide additional confinement after the first crack occurred, thus delaying the strength degradation of the structure. Three two-third scale space frame corner beam-column joint subassemblies were also constructed to investigate the biaxial loading effect. Two specimens were deep-deep beam-corner column joint specimens and the other one was deep-shallow beam-corner column joint specimen. One deep-deep beam-corner column joint specimen was not using any transverse reinforcement in the joint core while the two other specimens were using one transverse reinforcement in the joint core. Plain round longitudinal bars were used for all units with hook anchorage for the beam bars. Results from the tests confirmed the evidences from earthquake damage observations with the exterior 3-D (corner) beam-column joint subjected to biaxial loading would have less strength and suffer higher damage in the joint area under earthquake. Furthermore, the joint shear relation in the two directions is calibrated from the results to provide better analysis. An analytical model was used to simulate the seismic behaviour of the joints with the help of Ruaumoko software. Alternative strength degradation curves corresponding to different reinforcement detailing of beam-column joint unit were proposed based on the test results.

This thesis focuses on the seismic behaviour of reinforced concrete structures with masonry infills, with particular interest in the development of rational procedures for the design and analysis of this type of structure. The properties of masonry and its constitutive materials were reviewed, giving special emphasis to those aspects which contribute to a better understanding of the strength mechanism. Theoretical procedures were developed for the rational evaluation of the strength of masonry subjected to compressive and shear stresses. A large amount of experimental work related to the behaviour of infilled frames was also reviewed. The main characteristics of the response under lateral loading were discussed for different types of infilled frames and a comprehensive classification of the modes of failure, for both the masonry panel and the surrounding frame, was conducted. In addition, the influence of several parameters which can affect the structural response was evaluated. Two theoretical procedures, with different degree of refinement, are proposed in this study for the analysis of infilled frames. The first procedure is a simple approach, based on the equivalent truss mechanism, which allows the evaluation of the lateral resistance of the infilled frames, considering two different types of failure in the masonry panel, namely, shear-friction and diagonal tension failure. The compressive strength of the diagonal strut is assessed by transforming the shear failure envelope obtained from the modification of the Mann and Muller's theory. This transformation takes into account the inclination of the diagonal strut and neglects the effect of the tensile principal stresses acting on the masonry panel. The second procedure is a refined macroscopic model based on a multi-strut formulation, which is intended to represent more accurately the effect of the masonry panel on the surrounding frame. Since debonding of the mortar joints is the most common type of failure observed in the masonry panel, the formulation of the procedure is specifically developed to represent this situation. The model accounts separately for the compressive and shear behaviour of masonry using a double truss mechanism and a shear spring in each direction. Recommendations are also given for the analysis of infilled frames when a failure due to diagonal tension or crushing of the corners is expected in the panel. A test programme was implemented to investigate the seismic response of infilled frames. The main criterion followed for the design was that the reinforced concrete columns should yield in tension in order to obtain a reasonable ductile response under lateral loading. New reinforcing details were provided in one unit, aimed at enhancing the structural response. These details consisted in tapered beam-column joints with diagonal reinforcement, and additional longitudinal reinforcement in the frame members. The additional bars placed in the columns were not anchored to the foundation in order to produce a weak region at the base of the columns, where most of the plastic deformations were expected to occur. The most important conclusion of the experimental programme is that the response of reinforced concrete frames with masonry infills can be significantly improved by a rational design aimed at reducing the distortion of the masonry panels while plastic deformations arc concentrated in selected regions of the structure. A new design approach is proposed for infillcd frames, in which two cases are considered: cantilever and squat infillcd frames. In the first case, the ductile behaviour is achieved by yielding of the longitudinal reinforcement, which is limited to occur only at the base ofthe columns, and by avoiding large elongations of the remaining parts of the surrounding frame. A pre-cracked connection is induced between the infilled frame and the foundation, where plain round dowels can be placed to control shear sliding. In the second case, ductility is conferred to the structure by allowing controlled sliding of the infillcd frame over the foundation. The applicability of this approach is limited to those cases where the total shear force exceeds the frictional strength of the pre-cracked connection. The effectof pinching of the hysteresis loops in the response of infilled frames subjected to earthquakes was investigated. A parametrie study was conducted using a one-degree-of-freedom oscillator subjected to ground accelerations recorded in five different earthquakes. Results obtained from the dynamic nonlinear analyses indicated that the effect of pinching and the damping model used can significantly influence the response of infilled frames, which normally exhibit a short to medium initial period of free vibration. Therefore, the displacement demand imposed by the earthquake can be larger than that assumed by the seismic codes if they are based on the concept of equal displacement.