The primary objective of this thesis was to study how the behavior of flexure-dominated masonry shear-wall segments is affected by changes in the normalized axial load and the percentage of vertical reinforcement. Six reinforced masonry shear-wall segment were constructed and tested at the Ferguson Structural Engineering Laboratory of the University of Texas at Austin. Specimens were 96-in. wide and 96-in. high (aspect ratio equal to 1.0) and were tested with different combinations of axial load ratio (zero and 0.10) and vertical reinforcement ratios (0.33% and 0.16%). Specimens met the 2011 MSJC Code requirements for special reinforced masonry shear walls, and were tested under quasi-static in-plane reversed cyclic loads. The specimens exhibited predominantly flexural behavior, as expected. Specimens exhibited high displacement ductility (5.6 to 16.7), as expected for flexure-dominated specimens. Specimens constructed with “green” units behaved essentially like otherwise identical specimens constructed with conventional (“gray”) units. / text

Most models developed for hydraulic fracturing in unconsolidated sands are based on Linear Elastic Fracture Mechanics (LEFM) and tensile fracture (Mode I fracture). However, in unconsolidated sand formations the field data shows that LEFM based models cannot properly predict the fracture behavior. Hydraulic fracture lab experiments in a true triaxial setup which was made as a part of this study are designed to investigate the failure mechanism around the crack tip in unconsolidated sands and effects of fluid rheology, leak off, and stress state are investigated. The results show that two mechanisms of tensile and shear failure are involved in fracture propagation in unconsolidated sands and depending on the fracturing fluid rheology and stress state of the formation one or both of them can happen at the crack tip. Several experiments with different fracturing fluids, rates, and different stress boundary conditions are categorized into two major categories based on whether we have a fracture or not. A subsequent categorization is used to categorize the fractured cases into Tensile Failure, Shear Failure and Mixed Failure categories. First the experimental observations are presented and subsequently observations are analyzed and compared in order to explain the observations and conclusions. ;Tensile failure category is happening in medium viscosity fracturing fluids in the order of 20,000 cP viscosity at unit 1/s shear rate. Shear failure category is mostly taking place in low viscosity fluids (200 cP viscosity at unit 1/s shear rate). Mixed mode fracturing is happening in high viscosity fluids (70,000 cP viscosity at unit 1/s shear rate) with high stress anisotropy. However, the same fluid will give a No Fracture result in the case of isotropic or near isotropic stress state. It is shown that higher stress anisotropy increases the tendency of shear failure and at the same time, the resulting fracture will propagate in a preferential direction. However, tilting and branching might happen due to high stress anisotropy which is more pronounced in case of thicker fluids. It was also observed that in case of vaseline injection, stress anisotropy decreases treatment breakdown pressure. / text

Development of shear databases attracted a great deal of attention in the shear research community within the last decade. Although a few shear databases have already been developed by several research groups, there is no comprehensive shear database that is focused on prestressed concrete members. This thesis aims to develop a shear database for prestressed concrete members with an intensive literature review. This literature review resulted in a database that contained a total of 1,696 tests reported in North America, Japan, and Europe from 1954 to 2010. The database was used to evaluate shear design provisions available in North America, Japan, and Europe. The variations in measured versus calculated shear strength using twelve shear design equations were analyzed. The analysis results indicated that design expressions based on the Modified Compression Filed Theory (MCFT) produced the best performance to estimate the shear strength of prestressed concrete members with sufficient shear reinforcement. The MCFT-based design expressions, however, provided unconservative strength estimations for members that failed in shear but exhibited signs of horizontal shear damage and/or anchorage zone distress. The ACI 318-08 detailed method was found to be less conservative than the MCFT-based design expressions. Additionally, on the basis of a careful examination of test results included in the database, a new limit for the minimum shear reinforcement was proposed. The database was also used to investigate the shear behavior of prestressed concrete members. This investigation revealed that there was no evidence of size effect in the shear strength of prestressed concrete members with sufficient shear reinforcement. Additionally, it was found that prestress force and shear reinforcement increased the shear strength although there was an upper limit on the effectiveness of shear reinforcement. / text

Pretensioned concrete box beams have been used in highway bridges for more than half a century. Due to their geometry, they have often been used as a viable alternative to the classic I-shaped girders. Box beams are highly effective in cases where speed of construction is a priority. However, the detailing and design of box beams are more complicated than that of I-shaped girders. The flow of forces at the beam’s end blocks must be understood in order to detail reinforcement adequately. The following were the objectives of this research study: (i) quantify the demands placed on box beam end blocks upon prestress transfer, (ii) characterize the demands placed on box beam end blocks upon the application of superimposed loads, (iii) evaluate the effects of alternative void geometries at skewed ends of box beams on curing temperatures, (iv) based on the knowledge gained in (i), (ii) and (iii), improve the box beam end blocks, (v) test the improved end block under worst case scenario demands at prestress transfer and under extreme loading conditions, and (vi) validate currently used shear strength design methodologies in their application to pretensioned box beams. In order to achieve these objectives, an experimental program was conducted. The experimental program included the load testing of ten 4B28 and five 5B40 box beams, for a total of twenty nine load tests. The influence of several factors that distinguish box beam behavior from the better-understood I-shaped girder behavior was studied. Additionally, the experimental program included the fabrication, instrumentation and early-age behavior study of five 5B40 box beams. The first three beams were used to vii assess the behavior of box beams fabricated with the current TxDOT standard details (from December 2006). The fourth beam incorporated modifications to the standard reinforcement details based on the observations made through the study of the first three 5B40 box beams. The last specimen corresponded to a new box beam cross section (5XB40) optimized to be used in a spread-box beams configuration. / text

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Methods for the design of steel frame/wood panel shear walls used as a seismic force resisting system have been developed. These methods, which can be used in conjunction with the 2005 NBCC, were based on the results of shear wall tests carried out using lateral loads alone. The research program was extended to determine the influence of gravity loads on the lateral performance of the shear wall. An initial series of stud column tests was completed to determine an appropriate predication method for the axial capacity of the principal vertical load carrying members. Recommendations for appropriate effective length factors and buckling lengths were derived from the results of 40 tests. A subsequent series of five single-storey shear wall configurations were designed using capacity based methods. These shear walls were tested under monotonic and cyclic lateral loading, where two of three shear walls were also subjected to a constant gravity load. In total, 32 steel frame/wood panel shear walls composed of 1.09--1.37 mm thick steel studs sheathed with DFP, CSP or OSB panels were tested and analyzed. The equivalent energy elastic-plastic analysis approach was used to determine design values for stiffness, strength, ductility and overstrength. The data from this most recent series of tests indicates that the additional gravity loads do not have a detrimental influence on the lateral behaviour of a steel frame/wood panel shear wall if the chord studs are designed to carry the combined lateral and gravity forces following a capacity based approach. A resistance factor of 0.7 was found to be in agreement with previous tests that did not include gravity loads. The calculated seismic force modification factors also agreed with the previous test results, which suggest that Rd = 2.5 and Ro = 1.7.

The MIDPLY shear wall has been developed to be used as a structural system for severe earthquakes. This type of construction has emerged as a viable alternative to concrete and steel for non-residential buildings. The MIDPLY shear wall utilizes a novel arrangement of sheathing and framing members with a special nailing technique. The MIDPLY joints have a different failure mode from that which is observed in standard shear walls. The study reported in this thesis focuses on the response of the MIDPLY shear wall due to monotonic and cyclic tests; the response of an increase size in the cross-section members of the MIDPLY shear wall; and also the evaluation of the design and performance of hold-down connections at the boundary end studs of the MIDPLY shear wall. Previously tested MIDPLY shear walls showed that the boundary end stud hold-down connection is a very critical component in the performance of the MIDPLY shear wall. After a simplified analysis of 2 possible hold-down connections (see Fig. 7, 8, 9 and 10), hold-down connection #2 was selected as the most viable option since it had the ability to withstand large lateral forces. For non-residential buildings we expect a larger lateral force when compared to residential buildings. Therefore the cross-section of the members in the MIDPLY shear wall was increased and the number of boundary end studs was modified. These measures resulted in an increase in the lateral force capacity with the use of hold-down connection #2. The experimental results were used to verify an analytical model representing the MIDPLY shear wall in load-displacement characteristics. Recommendations and future research will also be discussed to show the way for further performance optimization of the wall system.

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