This thesis emphasizes the critical importance of crack control in designing and constructing reinforced concrete (RC) structures. Cracks in such structures can significantly reduce strength and durability, pose safety risks, and lead to high repair costs. Existing codes and standards offer varying approaches, resulting in inconsistent results in designing for serviceability limit state (SLS). The evolution of modern reinforced concrete, incorporating additives like superplasticizers and silica fume, requires an update to crack control models based on outdated conceptions. The thesis aims to compare crack width calculations, understand bond stress in contemporary concrete models, and enhance crack control models. The study covers crack development, mathematical aspects of crack design, laboratory testing, and analysis of RC specimens. The findings aim to offer valuable recommendations and improve crack control measures, contributing to a more robust database and aiding the development of effective global model codes and standards for crack control in RC structures.:1. Introduction 2. General knowledge of cracks in RC structures 2.1. Cause of crack formation 2.1.1. Crack during the hardening process 2.1.1.1. Plastic shrinkage cracks 2.1.1.2. Plastic settlement cracks 2.1.2. Crack of hardened concrete 2.1.2.1. Drying shrinkage cracks 2.1.2.2. Thermal cracks 2.1.2.3. Crack due to chemical reaction 2.1.3. Crack due to external loads 2.2. Crack development in an axially loaded member 3. Crack width calculations 3.1. Design formula according to EN:1992 3.1.1. Calculating crack width 3.1.2. Calculating minimum reinforcement 3.1.3. Detailing of reinforcement 3.2. Design formula according to fib Model Code 3.2.1. Crack width calculation per fib Model Code 1990 3.2.2. Crack width calculation per fib Model Code 2010 3.3. Design formula in other codes and standards 3.3.1. Crack width calculation in American standard (ACI) 3.3.2. Crack width calculation in British standard (BS) 3.3.3. Crack width calculation in Vietnamese standard (TCVN) 3.3.4. Summary and example of crack width calculations a. Crack control per EN 1992-1-1 b. Crack control per Model Code 1990 c. Crack control per Model Code 2010 d. Crack control per ACI e. Crack control per BS f. Crack control per TCVN 4. Pull-out experiments 4.1. Experimental basis 4.2. Experiment setup 4.2.1. Test machine 4.2.2. Test cubes 5. Results and Discussion 5.1. Failure modes and bond-slip curves 5.2. The bond-slip functions 6. Conclusion 7. References

Lateral forces generated by wind, earthquakes, and other horizontal loads are trans-mitted from the floor diaphragms to the columns and walls that comprise the vertical lateral force resisting system in a building. Strengthening of the diaphragms in older reinforced concrete buildings may be necessary for several reasons, including to enhance seismic performance, address inadequate strength or stiffness, provide missing or incomplete load paths, improve inadequate shear transfer/connection capacity, and to accommodate changes in the use and occupancy of the structure. Engineers are currently using externally bonded fiber reinforced polymer (FRP) composites to retrofit deficient diaphragms. However, this application is beyond the scope of current FRP-related design documents, including ACI PRC-440.2R-17 "Guide for the Design and Construction of Externally bonded FRP Systems for Strengthening Concrete Structures". The lack of consensus around design recommendations for FRP strengthening of diaphragms is problematic and creates uncertainty about which approaches are proven and what are best practice. This thesis summarizes the results from an experimental research program designed to investigate the shear behavior of reinforced concrete diaphragms strengthened using external-ly bonded FRP. Six one-half scale reinforced concrete cantilever diaphragms were tested in shear to evaluate the influence of FRP material, density, spacing, orientation, and intermediate anchorage configuration on the performance of diaphragm strengthening. The specimens were designed to represent the diaphragm shear zone adjacent to a shear wall in a concrete building. The tests were performed using a reverse cyclic displacement protocol representative of earthquake actions. The tests included a baseline unretrofitted concrete specimen, followed by five retrofitted specimens with different configurations of externally bonded FRP. Each retrofitted specimen was designed to maintain a similar FRP axial stiffness while varying the FRP retrofit parameters. The results demonstrated that externally bonded FRP retrofitting improved both the shear strength and stiffness of the strengthened test specimens. All the retrofitted specimens experienced an FRP debonding failure initiated by intermediate shear cracks with the field of the diaphragm, occurring after yielding of the internal steel rebar. The results highlighted that the overall behavior of the specimens was influenced by the way the retrofit schemes were proportioned and detailed. For example, the application of FRP parallel to the direction of applied shear was found to be most effective at increasing the diaphragm strength. Conversely, the application of FRP perpendicular to the applied shear was found to increase the diaphragm ductility. In addition, the shear strength contribution of externally bonded FRP was significantly influenced by the retrofit surface coverage. Compared with narrow strips of high-density fabric, retrofits detailed with less dense fabric spread uniformly over the surface exhibited superior performance due to better control of the shear cracks. Furthermore, no meaningful difference in performance was observed between diaphragms strengthened with glass and carbon FRP composites, provided the retrofits were proportioned to achieve com-parable levels of stiffness. This finding suggests that either type of fabric may be suitable for diaphragm strengthening. Finally, the use of overstrength intermediate FRP anchors did not noticeably affect the FRP shear strength contribution. However, the presence of intermediate anchors led to localized failures that concentrated inelastic diaphragm response between anchor locations, resulting in a significant reduction in diaphragm deformation capacity. The test results were used to develop design recommendations for shear strengthening existing concrete diaphragms using externally bonded FRP. The recommendations included guidance on how to establish the effective FRP design strain and the nominal shear strength contribution of the FRP, both of which tended to be conservative and underestimated the actual behavior observed during the experiments. The recommendations also address the use of intermediate and end FRP anchors, limitations on the clear spacing between sheets, and other factors pertinent to retrofit design. / Master of Science / The floor diaphragm in a reinforced concrete building transmits lateral forces generated by wind, earthquakes, and other horizontal loads to the building's vertical lateral force resisting system. Diaphragms in older reinforced concrete buildings are often retrofitted to meet seismic demands. Retrofitting deficient diaphragms increases infrastructure sustainability by promoting reuse and reconfiguration of existing buildings while mitigating structural deficiencies. Using externally bonded fiber reinforced polymer (FRP) composites is a com-mon strengthening technique often used without supporting guidance or test data. An industry need for diaphragm retrofit provisions, coupled with a substantial lack of data clearly indicates a need for experimental testing of diaphragm elements strengthened with externally bonded FRP. This thesis summarizes the results from an experimental research program designed to investigate the shear behavior of reinforced concrete diaphragms strengthened using externally bonded FRP. Six reinforced concrete diaphragm specimens were tested to study how variations in FRP material, density, spacing, orientation, and anchorage configuration impacted the performance of the retrofit. One specimen served as a control while the five other specimens were retrofitted with various configurations of FRP. The control specimen experienced a diagonal tension shear failure while each FRP strengthened specimen exhibited an FRP debonding failure, which was initiated by intermediate shear cracks occurring within the field of the diaphragm. The experimental results were analyzed to understand how the FRP retro-fits affected the strength, stiffness, ductility, and energy dissipation of each specimen. It was concluded that externally bonded FRP improves the seismic performance of a building by increasing the in-plane shear strength of the diaphragm. Existing design provisions were evaluated and compared to the experimental findings. Design recommendations were formed based on the observed affect of the test variables.

Page 190 was not included in the thesis. / <p> A research program is presented for assessing the plastic collapse load and shake-down load of reinforced concrete continuous beams. This investigation attempts to establish a range of validity of simple plastic theory when applied to the under-reinforced concrete beams and to determine the sensitivity of such structures to variable repeated loading. In attempt for more accurate prediction of the behaviour of reinforced concrete beams when subjected to variable repeated loading, the numerical beam analysis was developed.</p> <p> An experimental program was conducted on 10 reinforced concrete continuous beams. Deflections and strains of these specimens of nearly prototype size were measured and compared with predicted values at critical cross-sections. Resulting conclusions and recommendations for further research are made.</p> / Thesis / Master of Engineering (MEngr)

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This dissertation covers concrete and cement paste (CP) containing portland-limetsone cement (PLC) for the purpose of understanding mainly mechanical property behaviors. PLC has been consistently investigated by researchers over the past decade who have found equal and often superior performance with PLC, but few researchers have found reasons why. Throughout this dissertation CP cylinders are used to help understand concrete. By understanding the CP (cementitious materials, water, admix, and no fine or coarse aggregates) portion of concrete, it is believed further understanding can be achieved. The interaction of CP and aggregates, or paste aggregate bond (PAB), is exceptionally important. Literature review suggests PAB can be affected by chemical and physical properties of aggregates as well as cement which dictates the mechanical property performance of concrete. CP measurements used herein are mainly compressive strength, however there were other measurements, such as thermal setting, collected as well. CP properties whether thermal or mechanical, generally agreed with concrete results. Additionally, CP compressive strengths were found to have value beyond what was previously known. Mainly that CP compressive strengths can help diagnose concrete behavior. CP used with concrete measurements can give some indication, not previously available, concerning PAB and bonding efficiency. However, the CP measurements had high variability. As such, a new CP production method was developed alongside different analysis techniques to reduce the variability. CP was further used with concrete to recommend a factor for balancing fineness and limestone percentage in PLC. Next, CP measurements were used with 74 concrete mixtures for investigating the Mississippi Department of Transportation fly ash replacement level limits for ordinary portland cement (OPC) and PLC for implementation into the Mississippi market. Lastly, this dissertation delved into non-production concrete mixtures with few ingredients (washed aggregates, cementitious materials, and water) to discover mechanisms behind PLC and OPC behaviors. From CP and concrete measurement perspectives, it is recommended that PLC in the MS marketplace be implemented without hesitation. From the conclusions herein, there does not appear to be many cases where OPC considerably outperforms PLC. In almost every case, PLC performs equivalent or better than OPC when numerous properties are considered.

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