This thesis presents a finite element (FE) modelling approach investigating the effects of corroded shear reinforcement on the capacity and behaviour of shear critical reinforced concrete (RC) beams. Shear reinforcement was modelled using a “locally smeared” approach, wherein the shear reinforcement is smeared within a series of plane-stress concrete elements at the specific stirrup location. This was done with the objective of incorporating both the reduction in cross-sectional area due to corrosion and the corresponding expansion of corrosion products build up. Corrosion damage was incorporated through equivalent straining induced by the corrosion build up on the affected surrounding concrete where the concrete cover was treated as a thick-wall cylinder subjected to internal pressure. Strains were introduced in the FE model using fictitious smeared horizontal pre-stressing steel, with a compressive pre-straining level related to the degree of corrosion penetration of the reinforcement. The FE modelling approach was first validated against published test data of shear critical RC beams with and without stirrup corrosion. The proposed modelling approach successfully reproduces the load deformation response as well as the failure mode and cracking patterns of the published experimental tests. Upon validation of the FE model, the work was extended to a parametric analysis of important shear design variables, such as the shear span-to-depth ratio, beam width and stirrup spacing The FE analyses were carried out for three increasing levels of corrosion (low, moderate and high) applied to affected stirrups within the critical section of the beams and based on steel mass loss (10%, 30% and 50%, respectively). In general, the results show a reduction in load carrying capacity accompanied by a softening of the load-deformation curves with each increasing level of corrosion. In most of the cases, a reduction in deflection associated to peak loads was also observed for moderate and high levels of corrosion. The impact of the various parameters was studied with respect to strength and deformation, as well as crack angle and mid-height horizontal strain. This was done in an effort to compare FE values to those provided by the CSA A23.3 design equations. The CSA A23.3 shear design equations were compared against FE analysis data in terms of residual shear strength estimation and individual component contributions to shear resistance (i.e., concrete and steel). The comparisons revealed an over conservative estimation for both strength and concrete contributions and an overestimation of the steel contribution. This divergence was attributed to a transition in shear behaviour within the critical section. Based on the progression of the concrete compressive struts with increasing corrosion and predicted crack angle, it was found that stresses in affected sections are redistributed towards adjacent undamaged material. The shear resistance mechanism generally transitioned from typical beam behaviour towards an arching-dominated one. Finally, based on important findings from the literature and the work conducted within this research, important considerations for assessment practice are suggested.

Based on previous testing and analysis, it is believed that North American concrete design codes yield conservative shear designs for precast/prestressed hollow-core slabs in the 203 to 305 mm depth range. The objective of this research program is to calibrate the Canadian code shear equations to precast/prestressed hollow-core slabs, through testing a series of full-scale slabs to failure in shear. A total of twelve hollow-core slabs from one slab producer, using two types of extruders were tested in shear. Test variables include the bearing length and the prestressing level. Results are presented in terms of experimental to predicted capacity using the Canadian and American concrete design codes, the failure mode, crack profiles, and the critical section location for shear. It was concluded that the Canadian code shear equations are inappropriate for use with hollow-core slabs with low prestressing levels in the 203 to 305 mm depth range.

Objective: To evaluate the effect of an in-office plus at-home bleaching protocol on shear bond strength of orthodontic buttons when using a fluoride-releasing sealant. Methods and Materials: One hundred and sixty extracted human molars were randomly divided into bleached (N=80) and unbleached groups (N=80). The bleached group was treated with 45% carbamide peroxide for half an hour, followed with five applications of 20% carbamide peroxide at 24 hour intervals. After two weeks, lingual buttons were bonded on the teeth in both groups using either Transbond XT primer or Pro Seal sealant. The teeth were then stored in artificial saliva and subjected to shear testings at 24 hours and 3 months using a Zwick Universal Test Machine. Results: The ANOVA analysis of the 24-hour results indicated a significant difference between the four subgroups (p<.0011). Further simple t-tests indicated that the differences were significant only between bleached and unbleached subgroups (p<.0011). The 3-month results showed the mean shear bond strengths of the unbleached group using Pro Seal sealant was statistically significantly lower than the others although still greater than clinically minimal suggested bond strengths. Interestingly, 15% of the bleached teeth exhibited enamel fracture at the 3-month testing. Conclusion: At 24 hours, both Pro Seal sealant and Transbond XT primer appear to be a reliable choice on both bleached and unbleached teeth. However, at the 3-month period, Pro Seal sealant yielded significantly lower shear bond strength on unbleached teeth, nevertheless well within the range of values considered to be "clinically acceptable".

A search for the effects of anisotropy on seismic body-waves predicted by theory is described. Preliminary studies were based on long-period data from the WWSSN, HGLP and SRO networks. These showed that data from the WWSSN network are unsuitable for anisotropy studies because of features in the geometry of the recording system which lead to misalignment of the digitizer relative to the galvanometer-swing (which it is not always possible to correct) and the fact that the horizontal components are not always well matched. Digital data from the HGLP (recorded after 1976) and SRO networks are more suitable for anisotropy studies but eventually it was found that the anisotropic differences are too small to be resolved by long-period instruments. Analysis of short-period teleseismic shear-waves observed at LRSM stations located in United States and southern Canada has revealed shear-wave splitting diagnostic of anisotropy somewhere along the path. The shear-wave splitting is often seen as two separate shear-wave arrivals on the rotated horizontal components. All cases of shear-wave splitting are indicated by an abrupt change in the direction of particle-motion in the horizontal plane. A selection of seismograms and associated particlemotion diagrams is presented in order to illustrate shear-wave splitting. The polarizations of the first arrival shear-waves and the delays between the shear-wave arrivals were measured and are presented in the form of stereograms. The maximum shear-wave delay observed is 2.75 seconds and on the basis of this, we calculate the thickness of the anisotropic layer to be 248 kms for a model with 4.5% differential shearwave velocity anisotropy. For a model with much higher differential shear-wave velocity anisotropy (8.4%), the thickness of the layer is only 136 kms. Our results do not allow us to constrain the depth to the top of the anisotropic layer, although on the basis of other studies we believe the anisotropic layer to be situated immediately below the Mohorovicic discontinuity. The polarizations are broadly similar to those obtained theoretically for the y- and z-cuts of olivine, transversely isotropic olivine and mixture of transversely isotropic olivine/isotropic material. On the basis of this, we tentatively identify N50°E as a direction of symmetry and note that it is approximately parallel to the absolute motion of the North-American plate. We therefore suspect a causal relationship between plate motion and the generation of anisotropy. The most likely hypothesis is that as the continental lithosphere moves across the asthenosphere, the drag on the lithosphere sets up a horizontal compression in the direction of motion of the lithosphere relative to the asthenosphere and olivine crystals align by {Okl} [100] pencil glide so that the a-axis points into the direction of plate motion while the b and c axes form girdles perpendicular to the a-axis. This would result in transverse isotropy with the axis of symmetry horizontal, an orientation which is consistent with our results. The existence of anisotropy in the upper mantle has implications for other seismological studies. In particular, focal mechanism studies which rely solely on S-wave polarizations will be erroneous and studies of travel-time residuals will need to take account of the anisotropy.

Experiments were carried out to study the effect of workmanship and environmental conditions on bond strength for concrete patch repairs. Four repair materials, sand/cement mortar, acrylic modified cementitious mortar, SBR modified cementitious mortar, and flowing concrete, were tested with mainly three test methods (core pull-off test, patch compressive test, and patch flexural test). At the beginning of this project, slant shear tests were also carried out. In the study of the effect of workmanship, the following parameters were included: surface roughness, surface cleanliness, surface soundness, moisture condition, application method, bond coat mistiming, repair material mistiming, and curing methods. In the study of the effect of environmental conditions, four parameters were considered: high temperature curing followed by drying shrinkage, high temperature curing followed by thermal cycling, low temperature curing, and low temperature curing followed by freeze/thaw cycling. A rougher surface produces a higher bond strength, but the increase depends on individual repair material. Sand/cement mortar favours a rough surface, but polymer modified mortars are not very sensitive to surface roughness. Environmental conditions affect the bond strength development, but the effect varies with each repair material. Test results suggest that low temperature curing should be avoided for polymer modified cementitious mortars. In addition to the experimental study, theoretical analyses were carried out to evaluate the available bond test methods. The evaluation was concentrated on answering the following questions: (1) What kind of factors will influence conductinga bond test? (2) What are the response of each factor involved to a specific test method? (3) What kind of influences are crucial in ensuring the full development of the bond strength? (4) Which factors are important to achieve a durable repair? and (5) What kind of a test can be used to monitor the quality of these crucial factors? In total, about 800 tests were conducted (500 core pull-off tests, 90 patch compressive tests, 100 patch flexural tests, and 80 slant shear tests).

Shear-wave splitting is a phenomenon observed in almost all in situ rocks. Due to propagation through stress-aligned and fluid-saturated microcracks and fractures the initial shear wave splits into two almost orthogonal waves which propagate with different velocities along similar ray paths. The process is characterized by the polarization direction of the faster split shear wave, which is parallel to the orientation of the cracks, and the time delay between the onsets of the two waves. The analysis of shear-wave splitting has been conducted over records of 233 microearthquakes in the vicinity of five seismic stations in SW Iceland. Visual methods have been applied to the data to retrieve the final results for polarization directions and time delays. The main polarization azimuth for the leading split wave is N30°- 60°E which is in full agreement with the mapped alignments of normal faults and volcanic fissures in the surface. The time delays measured at different sites vary in the range of 10-100 ms for the events of best quality. In general, splitting times do not show a clear pattern at all recording sites with increasing depth. The only firm conclusion that can be drawn from the time delays is that at station BLF in the Brennisteinsfjöll fissure swarm, the time delays are smaller than in the Hengill area and therefore the strength of anisotropy beneath that station appears to be lower.

In 2011, Roger Xu (UToronto) carried out an experimental study to investigate shear reinforcement ratios required to cause crushing of diagonal struts in high-strength reinforced concrete I-beams. Xu’s experimental results were found to be inconclusive due to detailing issues resulting in flange splitting and web blow-out. This thesis outlines an experimental test programme completed in Spring 2012 to mitigate the issues encountered by Xu. Through experimental observation, data acquisition, and numerical analysis, the test program described in this thesis is shown to overcome the aforementioned issues. The study is expanded upon with an additional test series of rectangular beams aimed to examine the applicability of the maximum shear capacity provision of the Canadian Standards Association (CSA) A23.3-04 design standard. Test data suggests that the 0.25fc'bwdv upper limit for shear reinforcement used in CSA A23.3-04 cannot be reliably attained when using high strength concrete.

In 2011, Roger Xu (UToronto) carried out an experimental study to investigate shear reinforcement ratios required to cause crushing of diagonal struts in high-strength reinforced concrete I-beams. Xu’s experimental results were found to be inconclusive due to detailing issues resulting in flange splitting and web blow-out. This thesis outlines an experimental test programme completed in Spring 2012 to mitigate the issues encountered by Xu. Through experimental observation, data acquisition, and numerical analysis, the test program described in this thesis is shown to overcome the aforementioned issues. The study is expanded upon with an additional test series of rectangular beams aimed to examine the applicability of the maximum shear capacity provision of the Canadian Standards Association (CSA) A23.3-04 design standard. Test data suggests that the 0.25fc'bwdv upper limit for shear reinforcement used in CSA A23.3-04 cannot be reliably attained when using high strength concrete.

The use of fiber-reinforced polymer (FRP) composites as a repair and strengthening material for reinforced concrete (RC) members has increased over the past twenty years. The tendency for FRP sheets to debond at loads below their ultimate capacity has prompted researchers to investigate various approaches and designs to increase the efficiency of FRP strengthening systems. Various anchors, wrapping techniques and clamps have been explored to postpone and/or delay the debonding process which results in premature failure. FRP anchors are of particular interest because they can be selected to have the same material properties as the FRP sheets that are installed for strengthening or repair of the RC member and can be done so using the same adhesives and installation techniques. This research study aimed to investigate the effectiveness of using commercially manufactured FRP anchors to secure FRP sheets installed to strengthen and repair RC beams in shear and RC slabs in flexure. Twenty one shear critical RC beams were strengthened in shear with u-wrapped FRP sheets and FRP anchors. Eight RC one-way slabs were strengthened in flexure with FRP sheets and FRP anchors. The test variables include the type of FRP sheets (GFRP,CFRP), type of FRP anchors (CFRP, GFRP) and the strengthening configuration. The test results of the shear critical RC beams revealed that the installation of commercially manufactured FRP anchors to secure externally applied u-wrap FRP sheets improved the shear behaviour of the strengthened beam. The installation of FRP anchors to secure u-wrapped FRP sheets provided an average 15% increase in the shear strength over companion unanchored beams and improved the ductility of failure experienced with the typical shear failure in beams. The use of FRP anchors allowed the FRP sheets to develop their tensile capacity. Premature failure by FRP debonding was eradicated with the presence of FRP anchors and the failure modes of the strengthened beams with FRP anchors was altered when compared to the companion unanchored beam. Additionally, as the width of a u-wrapped FRP sheet was increased; larger increases in strength were obtained when FRP anchors were used. The test results of the flexure critical RC slabs revealed that the installation of commercially manufactured FRP anchors to secure externally applied u-wrapped FRP sheets improved the behaviour of strengthened slabs. Installation of FRP anchors to secure flexural FRP sheets provided an average 17% increase in strength over companion unanchored beams. The use of FRP anchors allowed the FRP sheets to develop their full tensile strength. Premature failure by CFRP debonding was not eliminated with the presence of FRP anchors; rather the critical failure zone was shifted from the bottom soffit of the slab to the concrete/steel rebar interface. The failure modes of slabs with FRP anchors were altered for all specimens when compared to the companion unanchored slab. The effective strain in the FRP sheet was predicted and compared with the experimental results. The efficiency of FRP anchors defined as the ratio of effective strain in the FRP sheet with and without anchors was related to the increase in strength in beams and slabs. A good correlation was established between the FRP anchor efficiency and the increase in strength. A step-by-step FRP anchor installation procedure was developed and a model to predict the number of FRP anchors required to secure a FRP sheet was proposed. This is the most comprehensive examination of beams and slabs strengthened with FRP sheets and FRP anchors conducted to date. This study provides an engineer with basic understanding of the mechanics, behaviour and failure modes of beams and slabs strengthened with FRP sheets and anchors.

No description available.