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Reinforced concrete columns are essential elements that are responsible for overall strength and stability of structures. Loss of a column within a frame can cause progressive collapse. While some research has been conducted on blast performance of reinforced columns, primarily under far-field explosions, very limited work exists on the effects of close-in explosions. Dynamic response of concrete columns, in multi storey building, was investigated under close-in blast loads numerically, using FEM software LS-DYNA. A six-storey reinforced concrete building was selected for this purpose. Different standoff distance/charge mass combinations were used to investigate the failure modes of external building columns. Three different charge masses were used; i) backpack bomb having 22.67 kg (50 lbs) of TNT, ii) compact sedan car bomb with 227 kg (500 lbs) of TNT and iii) sedan car bomb with 454 kg (1000 lbs) of TNT. The explosives were placed at different distances relatively close to the structure, triggering different failure modes. Effects of transverse reinforcement and column location (edge versus corner column) were studied under different combinations of charge weight and standoff distance. Column response under dynamic blast load was identified as either local or global. The results show that the failure mode with backpack bombs located at small standoff distance is either local breaching or concrete scabbing. Direct shear failure occurred at column supports when higher charge masses were detonated at close distances. As the standoff distance increased the response changed from breaching or direct shear to diagonal tension and flexure. The column transverse reinforcement played a major role in controlling diagonal shear cracks and promoting flexural response. Hence, the amount and spacing of transverse reinforcement were observed to be important design parameters.

The research on headed stud connections described in this thesis forms a part of a larger program with the objective of predicting the behaviour of precast concrete panel buildings under earthquake loads. The first objective of this research is to produce experimentally a concrete failure of the connection and to compare the actual failure load to the one predicted by the PCI design handbook. The tests show that the PCI shear-tension interaction equation for single headed studs can be used for the prediction of a concrete failure for a connection of the type tested. This method yields conservative results if a special equilibrium model for the determination of the stud tension force is used, and the bearing capacity of the structural steel angle on the concrete is neglected. The second objective of this research is to determine the bearing capacity of a reversed angle connection. Experiments show that this bearing capacity is equivalent to a force resulting from a stress equal to the concrete strength uniformly distributed over the concrete area enclosed by the structural steel angle 2" x2". Furthermore, the location of this force can be assumed in the center of gravity of the structural steel angle shape, regardless of whether or not there is an endplate present. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

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The present approach to the design of prestressed beams is antiquated and time consuming. Neither SLS or ULS requirements are satisfied directly. There is a need for a new approach using plastic principles to design the prestressing requirements at ULS considering a whole span at a time, with checks made for SLS requirements afterwards. For a plastic design, the designer would need to know the limits of the bending moment redistribution for the beam under consideration. An equation is therefore necessary to assist the designer in this regard. Such an equation should take into account the cross-section shape of the beam and the prestress to reinforcing steel ratios. Many examples would have to be investigated using a rigorous plastic analysis to formulate such an equation. A computer program has been written as part of this thesis to perform such a rigorous analysis. It's accuracy has been evaluated by comparison with laboratory test beam results. The comparison was favourable, although more results would have to be compared to establish the accuracy that could be expected. A few examples were investigated and the observations noted. Two extreme cases were examined, those of a T-beam and I-beam. The redistribution of bending moments was similar in both cases, but the percentage of the central moment capacity reached was considerably less for the T-beam. For both beams it was impossible to reach the ultimate capacity at the centre before the strain capacity at the supports was exhausted. It was concluded that a plastic design procedure should be introduced, based on the ULS capacity of a span at a time. SLS requirements could then be checked afterwards. This approach would provide a design procedure corresponding to those used for other forms of modern structural design and would be much quicker, safer, more accurate and less costly that the existing design procedures.

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A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science in Engineering, Johannesburg, 2019 / Premature deterioration of reinforced concrete railway bridges before and after repair is a serious concern as it is costly and poses a major risk on safety and performance. Reinforced concrete railway bridges in aggressive environments (near the sea) face the risk of ingress of corrosion agents (oxygen, moisture and chlorides) into the concrete to the reinforcing steel. Although, corrosion of the reinforcing steel is not the only cause of structural deficiencies in railway bridges, it is a significant contributor to deterioration and therefore of major concern. In order to guide the selection of a suitable repair option, one repair material from each category (patch repair mortars, barrier systems, electrochemical methods and corrosion inhibitors) was investigated. The effectiveness of selection was assessed by employing electrochemical techniques to quantify the performance of each selected repair material in stifling chlorideinduced corrosion in reinforced concrete. This study focuses on the evaluation of selected repair materials for chloride-induced corrosion in reinforced concrete using 100 x 100 x 500 mm long beam specimens. The four selected repairs were applied to the reinforced concrete beams after a period of 200 days after casting. The beams had a constant concrete cover to reinforcing steel of 20mm. The beam specimens were casted using admixed chlorides into the mix and were subjected to a cycle of 3 days wetting (with 5% NaCl solution) and 4 days drying. The beam specimens were monitored for half-cell potential (Cu/CuSO4), corrosion rate (coulostatic technique) and concrete resistivity (Wenner probe technique). Results indicate that the selected repair materials in this study had varied influences on the halfcell potential and corrosion rate values. The patch repair material replaced the concrete cover with a more durable material, confirmed from the Durability Index (DI) tests conducted. The resistivity of the repair mortar was measured to be higher than the concrete. Due to the replacement of the concrete cover, the corrosion rate values reduced when compared to the control reinforced beam specimens. However, the half-cell potential values indicated the probability of corrosion is still high after application. The barrier method, applied a silane-based sealer on the reinforced concrete beams. The resistivity of the concrete increased after application of the barrier method. The corrosion rates after application of the barrier method was lower than the corrosion rates of the control reinforced concrete beams. The half-cell potential results indicated the corrosion risk is still high after application of the barrier method. The electrochemical repair was the only repair material that showed more negative potentials than the control beams and corrosion rates were significantly higher than all the other repair methods after application. The reason for this can be attributed to the zinc anode dominating the potential and corrosion rate values. Therefore, no conclusion can be made on the corrosion condition of the reinforcing steel. Alternative methods should be employed in determining the effectiveness of sacrificial anode repairs. / PH2020

The seismic design of buildings is usually performed using one-way analysis for each of main axes independently. However, seismic events have fairly random behaviour and impose bidirectional solicitations on structures. In this work, the study of the response in structures subjects to earthquake loads with irregularity of l-shaped plan and soft story is carried out. For this, the linear time-story analysis (LTHA) of these has been carried out imposing seismic solicitations in two orthogonal directions. Thus, the structural response with incidence angle variations of 10 is obtained and compared with the response derived from the unidirectional analysis. Variations of up to 50% and 72% are obtained for model structures with l-shaped plan and soft story respectively.

Concrete compressive strength is one of the most important material properties affectingthe design of concrete structures. Strength that will be achieved once the concrete sets should be correctly predicted prior to pouring the concrete. Regression techniques can be used to calculate the 28-day concrete strength with a level of certainty. This thesis deals with the data modelling and analysis of 28-day compressive strength of high-performance concrete. Historical data on various mix compositions of high-performance concrete was obtained from University of California, Irvine repository. The data had 8 predictors and 1 response variable. In this thesis, three penalized regression approaches, namely, ridge, lasso, and elastic net were used to create a predictive model for compressive strength, and the performance of these model were compared to the traditional multiple linear regression model. Holdout sets from 2% to 40% at an increment of 2% were taken. Every regression algorithm was designed to conduct regression on 30 sets of randomly partitioned data. The performance of models was assessed using coefficient of multiple determination, RMSE, and residual plots. All regression techniques were able to predict the concrete strength with about 75% accuracy level.

The section of highway over the 400 South roadway in Orem, Utah is made up of two separate three span bridges. The bridges were originally constructed in 1960 and were expanded in 2004 to accommodate for one extra lane per bridge. During the fall of 2012 both bridges were scheduled for demolition and four girders were salvaged from the southernmost span of the 2004 expansion. These girders were transported to the Structural Materials And Systems Health Lab (SMASH Lab) where a series of tests were performed to determine the prestressing losses, flexural, shear, and shear-flexure capacity of the girders. The results of these tests were compared to the American Association of State Highway and Transportation Officials Load Resistance Factored Design (AASHTO LRFD) Bridge Design Specifications and an ANSYS Finite Element model. For all test results the AASHTO Bridge Design was conservative for each test setup and was able to predict the type of failure that occurred. The finite element model was developed for the four test conditions and calibrated so as to accurately represent test data. The calibrations were compared to actual tested material properties to determine the difference between the theoretical model and the girders. (120 pages)