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ANCHORAGE OF HIGH-STRENGTH REINFORCING BARS WITH STANDARD HOOKS By Ali Ajaam Submitted to the graduate degree program in Civil, Environmental, and Architectural Engineering and the Graduate Faculty of the University of Kansas in partial fulfilment of the requirements for the degree of Doctor of Philosophy Date Defended: April 3, 2017 ABSTRACT Hooked bars are often used to anchor reinforcing steel where concrete dimensions are not sufficient to provide the required development length for straight reinforcement, such as in external beam-column joints. The purpose of this study is to expand the understanding of the behavior of hooked bars in high-strength concrete and to develop design guidelines allowing for the use of high-strength reinforcing steel and high-strength concrete. In this study, 122 simulated beam-column joints were tested as a continuation of previous work at the University of Kansas. The test parameters included bar size (No. 5, No. 8 and No. 11), hook bend angle (90° or 180°), embedment length (5.5 to 23.5 in.), amount of confining reinforcement within the joint (no confining reinforcement to nine No. 3 hoops), location of the hooked bar with respect to member depth, hooked bar stresses (22,800 to 138,800 psi), concrete compressive strength (4,490 to 14,050 psi), center-to-center spacing between hooked bars (2 to 11.8db), number of hooked bars (2, 3, 4, or 6), arrangement of hooked bars (one or two layers), and ratios of beam effective depth to embedment length (0.6 to 2.13). Some specimens contained strain gauges mounted along the straight portion of the hooked bars and on the confining reinforcement within the joint rejoin. Test results from this study, along with test results from earlier work covering specimens without and with confining reinforcement, concrete compressive strengths between 2,570 and 16,510 psi, and bars stresses at anchorage failure ranging from 22,800 and 144,100 psi, were used to develop descriptive equations for the anchorage strength of hooked bars. The results of this study show that the current Code provisions overestimate the contribution of the concrete compressive strength and the bar size on the anchorage strength of hooked bars. The incorporation of the modification factors for cover and confining reinforcement in the provisions in the ACI Building Code (ACI 318-14) produces an unconservative estimation of anchorage strength of hooked bars, particularly with large hooked bars and closely-spaced hooked bars (hooked bars with center-to-center spacing less than 6db). Closely-spaced hooked bars exhibit less anchorage strength than widely-spaced hooked bars. The reduction in anchorage strength of closely-spaced hooked bars is a function of both the spacing between hooked bars and the amount of confining reinforcement. Both the hooks and the straight portion of hooked bars contribute to anchorage strength. The anchorage strength of staggered hooked bars can berepresented by considering the minimum spacing between the bars. Hooked bars anchored in beam-column joints with ratio of beam effective depth to embedment length greater than 1.5 exhibit low anchorage strengths compared to hooked bars with a ration below 1.5. These observations are used to develop proposed Code provisions for the development length of reinforcing bars anchored with standard hooks. The proposed provisions provide a higher level of reliability than current provisions and can be used for reinforcing steels with yield strengths up to 120,000 psi and concretes with compressive strengths up to 16,000 psi. Keywords: anchorage , beam-column joints, bond and development, concrete, high-strength concrete, high-strength steel, hooks, closely-spaced hooks, staggered-hooks, reinforcement, reinforcement strain منبع Ajaam_ku_0099D_15173_DATA_1.pdf

Failure analysis of RC shear walls with staggered openings under seismic loads تحلیل گسیختگی دیوارهای برشی بتن مسلح با بازشوهای شطرنجی در بارهای لرزه ای Marius Mosoarca a b s t r a c t Reinforced concrete shear walls are used to design buildings located in seismic areas, because of their rigidity, bearing capacity and high ductility. Until now many theoretical and experimental tests on shear walls with or without openings have been made, therefore their failure modes have been analysed and are rather very well-known; the research results being confirmed by real failure modes of RC walls after earthquakes. Design codes and standards based on the knowledge of the failure modes of the reinforced concrete walls were developed in order to obtain the ductile failure mechanisms. A special case is the failure mode of the reinforced concrete shear walls with vertical staggered openings. If at coupled walls the elements must be designed so that the plastic hinges appear at the ends of the coupled beams and then in the pier, this thing is more difficult at shear walls with staggered openings. Theoretical and experimental studies on structural walls with staggered openings, lamellar walls and walls with bulbs at the end have been made recently. There have also been studied the followings: the degradation of the stiffness, the ductility function to the intensity of the seismic force, the presence of the vertical forces, the position and the size of the openings and the reinforcing ways. The article presents the results of the theoretical and experimental tests on failure modes of three types of reinforced concrete shear walls with staggered openings which are compared to those obtained from walls with vertical ordered openings as far as the seismic response is concerned. The failure modes of the structural walls under seismic stress have been identified using calculus programs and cyclic alternated experimental tests. The theoretical research on the failure modes was the basis for the elaboration of a simplified methodology for the calculus of the maximum theoretical seismic force that produces the concrete crushing in the ultimate limit stage. The results theoretically obtained with the help of the calculus programs have been confirmed experimentally. The analysis of the failure modes, obtained with the computing methodology proposed, contributed to the completion of the seismic design codes for shear walls with staggered openings. منبع عملکرد_دیوارهای_برشی_بتنی_با_بازشوهای.pdf

The Importance of Determining Damage Levels of the Bridges in Non-Linear Dynamic Analysis Original Article, C30 Karimi Moridani K, Khodayari R, Asadpour M. Journal. Civil Eng. Urban. 3(4):191-196. 2013 ABSTRACT:During past earthquakes, different modes of damage were observed in bridges; consequently in seismic evaluation of these structures, various Indexes were used to determine vulnerability of the structures against earthquake vibrations. In this paper, damage indexes of structural elements of bridge are introduced and suggested definitions for structure damage state are stated. Then, a three span bridge is analyzed using OpenSees non-linear analysis software, considering three-dimensional model under earthquake load and non-linear behavior. After calculating necessary outcomes of the elements and nodes, damage indexes of damage at the foundations and columns level were measured. The model is able to calculate responses and damage indexes of supports and joints. Using this model, damage level of bridge structure is determined based on tables, which determine necessity of retrofitting. Based on the result, decisions made based on each criterion are compared. The results show that exact specification of damage indexes for the estimation of the vulnerability of structures (bridges here) is very important. Keywords: OpenSees Model, Bridge, Damage levels, Reinforcement, Stiffness منبع: [Hidden Content] دانلود: [Hidden Content].,30-191-196.pdf J. Civil Eng. Urban.,30-191-196.pdf

Cost Implication of Mitigating the Effect of Clay/Silt Content of Sand on Concrete Compressive Strength Oiginal Article, B25 Olanitori LM. J. Civil Eng. Urban. 2(4): 143-148. 2012. ABSTRACT: In Nigeria, reinforced concrete is one of the major building materials been used in the construction of buildings. In the specification of concrete, prescribed mix is normally used. However, tests carried out on different batches of concrete produced, using prescribed mix 1:2:4 of concrete show that the concrete did not acquire the 20N/mm2 expected strength at the age of 28 days. Depending on the type of sand used for the production of the concrete, the acquired strength after 28 days is between 25% and 60% of the expected strength. This reduction in strength will ultimately affect the functionality and durability of structure constructed from such concrete. To mitigate the effect of clay/silt content of sand, the sand can be washed free of clay/silt or the cement is increased in proportion to the percentage content of clay/silt in the sand. Since the mitigation of the clay/silt content of sand on concrete strength comes with extra cost, there is need to determine this cost in other to be able to build effective and safe structures. The author evaluates the cost implication of mitigating this reduction effect of the type of sand used on concrete strength. The extra cost incurred in the production of 1m3 of concrete (using mix ratio 1:2:4) in terms of washing the sand free of clay/silt is 22.5%, while that of cement increment is between 2.22% and 27.75% depending on the percentage of clay/silt content of sand. Mathematical models, which can be used to estimate the cost implication of this mitigation, are derived. Keywords:Reinforcement, Concrete, Sand, Silt, Strength منبع: [Hidden Content] دانلود: [Hidden Content],%20B25.pdf JCEU, B25.pdf