Browsing by Author "Durrani, Ahmad J."
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Item A computer-based tutor for engineering design(2000) PrakashGanesh, Prabhu; Durrani, Ahmad J.Modern computer technology facilitates development of rich learning environments that can enhance a student's ability to learn; however, none of the existing educational software systems can support the drill-and-practice mode of learning through the use of problem sets in routine engineering design domains. This thesis discusses the design of a computer-based system that benefits the instructor and the students in a design course by automating the creation of problem sets and their solution. The system allows the instructor to specify a set of design procedures as the design concept on which the generated problems should test the student. Each design procedure has a set of applicable conditions and these are formulated into a constraint satisfaction problem. Using the solution to this problem, the system then generates several problem descriptions along with their solution. The software, developed on a distributed component architecture model, is a general framework that could support multiple domains.Item Developing an introductory civil engineering course(1999) Spieler, Christof Torsten; Durrani, Ahmad J.A new course designed to introduce freshmen to civil engineering and to give non-engineers a taste of engineering was developed and taught. The course is divided into four sections (demand, design, construction, and effects) that illustrate the life-cycle of an engineering project. It was taught using case studies, illustrated lectures, discussions, and hand-on-projects. Extensive surveying of students indicates that the course was effective in conveying the importance of economics and inter-personal communications in engineering, portraying the scope of civil engineering, and giving students an understanding of the design process. Both engineers and non-engineers found the course interesting, and the engineering students felt that it encouraged them to remain in engineering.Item Effect of a slab on the behavior of exterior beam to column connections(1985) Zerbe, Hikmat Edward; Durrani, Ahmad J.; Lutes, Loren D.; Austin, Walter J.In reinforced concrete frame buildings, slabs are usually cast monolithically with the floor beams. The currently used recommendations for the design of beam to column connections for seismic loading, however, completely ignore the presence of the slab. Even though, previous studies have shown slabs to have a significant effect on the performance of connections, it has been believed that the test data are not adequate to justify revisions of the design recommendations. In this experimental investigation, the interaction of a slab with exterior beam to column connections is studied. The experimental program consisted of tests under simulated earthquake type loading on seven large-scale exterior beam to column connections. Except for the slab width, which was varied in each specimen, the basic design and configuration of subassemblages remained the same and conformed to the current design criteria. Based on the test results, it is concluded that it may be nonconservative to ignore the slab in the design of connections. It is suggested that a certain width of the slab effectively acts as a part of the floor beam. It is also concluded that at larger levels of interstory drift, transverse beams may not be effective in confining the joint. Ignoring either of these effects can lead to nonconservative connection designs.Item Effect of slab in inelastic analysis of R/C buildings under earthquake type of loading(1991) Yalcin, Usame; Durrani, Ahmad J.Tests on beam-to-column connections have shown that the presence of a slab significantly increased the flexural resistance of the beams under bending which caused tension in the slab. The presence of a slab in reinforced concrete buildings was studied both at the cross sectional and element modelling levels. At the cross sectional level, the experimentally observed progressive slab participation is recognized by a proposed strain distribution in the slab. The proposed strain distribution, along the flange width of a beam-slab section, accounts for the progressive increase in the slab participation with its changing pattern as a function of the strain level at the column face. The analytical prediction of the strain distribution in the slab agrees with the observed strain distribution in the slab of beam-column subassemblies. Furthermore, the increase in the yield curvature and hence a reduced postcracking stiffness of a beam-slab section resulting from the proposed strain distribution as compared with that of the uniform strain distribution is negligible. At the element level, the multi-spring model was modified to account for the recognition of different strength and stiffness in slab-in-tension and slab-in-compression directions of bending. Results from inelastic dynamic analyses of a typical multistory building with different slab participation suggest significant increases in story accelerations and base shears with increasing slab participation. The ductility requirements of the beams and columns are also significantly affected by the recognition of direction dependent stiffness in inelastic analyses. Due to a larger participation of the slab when in tension as compared with that in compression, the ductility requirement in slab-in-compression direction of the beams can get larger. Furthermore, the increased capacity of the beam-slab section affects the flexural and rotational ductility demands placed on the columns which can lead to a strong-beam and weak-column mechanism under lateral loading.Item Effect of transient high temperature on high-strength concrete(1987) Castillo, Carlos; Durrani, Ahmad J.The effect of transient high temperature in the uniaxial compressive strength of high strength concrete was investigated. The temperatures studied varied from 100$\sp\circ$ to 800$\sp\circ$C. The presence of loads in a structure was simulated by preloading the test specimens during the heating period. Results showed that exposure to temperatures between 100$\sp\circ$ and 300$\sp\circ$C decreased the compressive strength of high strength concrete by 15 to 20 percent. For temperatures between 400$\sp\circ$ and 800$\sp\circ$C,the compressive strength of concrete decreased to thirty percent of that at room temperature. One third of the preloaded specimens failed explosively during the heating period. In the remaining specimens the presence of a preload had a beneficial effect and a smaller loss of strength was observed compared to unstressed specimens. Exposure to high temperature caused the modulus of elasticity to decrease in all specimens regardlessly of the preload condition and the strength of concrete.Item Effective stiffness and punching failure of flat-plate structures(1990) Ding, Yun; Durrani, Ahmad J.The existing equivalent frame methods for lateral displacement analysis of flat-plate structures are one-value stiffness models which do not reflect the realistic response of structures. Based on the experimental data, the procedure for predicting the drift response of flat-plate structures is reviewed and an approach is proposed which accounts for the changes in the stiffness during the loading history. The application of the suggested procedure is demonstrated through examples. Punching failure in a flat-plate structure greatly changes the overall stiffness and results in moment redistribution between various members of the structure. This effect needs to be considered in the nonlinear analysis of flat-plate structures subjected to earthquake loading. A numerical procedure to account for the localized punching failure in calculating the response of flat-plate structures is developed. Furthermore, a hysteresis model suitable for slab-column connections is proposed on the basis of test results and implemented in a nonlinear dynamic analysis program.Item Experimental/analytical approaches to modeling, calibrating and optimizing shaking table dynamics for structural dynamic applications(1998) Trombetti, Tomaso; Conte, Joel P.; Durrani, Ahmad J.This thesis presents an Experimental/Analytical approach to modeling and calibrating shaking tables for structural dynamic applications. This approach was successfully applied to the shaking table recently built in the structural laboratory of the Civil Engineering Department at Rice University. This shaking table is capable of reproducing model earthquake ground motions with a peak acceleration of 6 g's, a peak velocity of 40 inches per second, and a peak displacement of 3 inches, for a maximum payload of 1500 pounds. It has a frequency bandwidth of approximately 70 Hz and is designed to test structural specimens up to 1/5 scale. The rail/table system is mounted on a reaction mass of about 70,000 pounds consisting of three 12 ft x 12 ft x 1 ft reinforced concrete slabs, post-tensioned together and connected to the strong laboratory floor. The slip table is driven by a hydraulic actuator governed by a 407 MTS controller which employs a proportional-integral-derivative-feedforward-differential pressure algorithm to control the actuator displacement. Feedback signals are provided by two LVDT's (monitoring the slip table relative displacement and the servovalve main stage spool position) and by one differential pressure transducer (monitoring the actuator force). The dynamic actuator-foundation-specimen system is modeled and analyzed by combining linear control theory and linear structural dynamics. The analytical model developed accounts for the effects of actuator oil compressibility, oil leakage in the actuator, time delay in the response of the servovalve spool to a given electrical signal, foundation flexibility, and dynamic characteristics of multi-degree-of-freedom specimens. In order to study the actual dynamic behavior of the shaking table, the transfer function between target and actual table accelerations were identified using experimental results and spectral estimation techniques. The power spectral density of the system input and the cross power spectral density of the table input and output were estimated using the Bartlett's spectral estimation method. The experimentally-estimated table acceleration transfer functions obtained for different working conditions are correlated with their analytical counterparts. As a result of this comprehensive correlation study, a thorough understanding of the shaking table dynamics and its sensitivities to control and payload parameters is obtained. Moreover, the correlation study leads to a calibrated analytical model of the shaking table of high predictive ability. It is concluded that, in its present conditions, the Rice shaking table is able to reproduce, with a high degree of accuracy, model earthquake accelerations time histories in the frequency bandwidth from 0 to 75 Hz. Furthermore, the exhaustive analysis performed indicates that the table transfer function is not significantly affected by the presence of a large (in terms of weight) payload with a fundamental frequency up to 20 Hz. Payloads having a higher fundamental frequency do affect significantly the shaking table performance and require a modification of the table control gain setting that can be easily obtained using the predictive analytical model of the shaking table. The complete description of a structural dynamic experiment performed using the Rice shaking table facility is also reported herein. The object of this experimentation was twofold: (1) to verify the testing capability of the shaking table and, (2) to experimentally validate a simplified theory developed by the author, which predicts the maximum rotational response developed by seismic isolated building structures characterized by non-coincident centers of mass and rigidity, when subjected to strong earthquake ground motions.Item In-plane cyclic response of reinforced concrete frames with unreinforced masonry infills(1995) Haider, Sarah; Durrani, Ahmad J.The in-plane cyclic response of reinforced concrete frames with unreinforced masonry infill was studied. Four full-scale reinforced concrete frame assemblies with masonry infills were designed and tested under reversed cyclic loading. The effect of panel aspect ratio and the stiffness of the infill relative to the frame were studied in terms of stiffness, strength, energy dissipation and failure mode. Based on the test results, an equivalent diagonal compression strut model was developed to represent the behavior of masonry infill bounded by a reinforced concrete frame and a simplified method for the linear-elastic analysis of R/C frames with masonry infills proposed. Using the experimental load-deformation plots, the hysteretic parameters relating to stiffness degradation, strength deterioration and pinching of the hysteretic loops were identified. These may be used to define the behavior of confined infills for the non-linear analysis of the infilled frames.Item Infill panel system for seismic strengthening of flat-plate buildings(2001) Humay, Francis Kam; Durrani, Ahmad J.Many existing flat-plate buildings are seismically deficient and pose a threat to life safety if subjected to ground motions of even low to moderate intensity. Failure in such structures is typically the result of punching failure at the slab-column connection. Because of this, performance-based retrofit procedures are needed to upgrade these non-ductile buildings. This investigation evaluated the use of lightweight pumice stone concrete (LWPSC) infill panels as a retrofit alternative for flat-plate buildings. Six four-tenth-scale slab-column subassemblies were designed and detailed based on ACI 318-63 and current performance-based testing requirements. Except for one bare frame specimen, all the subassemblies were retrofitted with prefabricated LWPSC infill panels and subjected to quasi-static loading conforming to FEMA 273. The geometry of the individual units was governed by weight limitations for handling and erection. Among the variables studied were connections between the slabs and the infill wall and the addition of uniformly distributed perforations (circular and rectangular openings). All of the retrofitted specimens had significant increases in both strength and stiffness over that of the bare frame. The behavior of the specimen with the infill panels not attached to the slabs was similar to that of a masonry wall without any connections to the frame. Although diagonal tension cracks formed within the recessed region, ultimate failure of the infill did not occur. Instead, frame-wall interaction transmitted large concentrated shear forces into the column that eventually contributed to failure of the longitudinal tension splice. The remaining subassemblies all had connections to the slabs and perforations within the wall. Specimens with circular holes experienced uniformly distributed cracking throughout the entire area of the infill wall. The chosen configuration, however, did not sufficiently weaken the wall, and shear failure of the column stopped the test. Because of its ductility and energy dissipation mechanism, the most promising infill panel configuration contained rectangular perforations. Two different reinforcement patterns were tested using rectangular openings. The addition of diagonal reinforcement between openings had the effect of increasing the yield strength of the wall as well as better maintaining post-yield deterioration.Item Infrared thermography for non-destructive identification of reinforcement in concrete(1994) Tchainikov, Mikhail V.; Durrani, Ahmad J.Infrared thermographic technique is investigated numerically and experimentally to identify reinforcing steel in concrete members. Other non-destructive techniques, such as the ultrasonic technique, are subject to errors due to large scatter in sound wave propagation velocity for the different components of concrete. Since thermal conductivity and heat capacity are less influenced by the composite nature of concrete, thermography remains a promising alternative. A finite element based numerical analysis demonstrated the feasibility of thermography as an evaluation technique for reinforcement in concrete. Based on the understanding developed from the numerical simulations, experimental tests were conducted in 10 concrete specimens containing bars of various sizes and clear cover. The temperature measurements with infrared probes on the surface of the specimens clearly identified the bars up to one inch clear cover. More refined processing and imaging technique are needed to identify bars at larger depth.Item MegaBank(2008) Guittard, Francis Gevrier; Durrani, Ahmad J.MegaBank explores the rise of "mega" financial institutions and their place in the urban environment. It is a projection of scale based on current trends, exploring the urban and architectural implications of this new "bigness" within the global city. MegaBank asserts a new relationship between trading floor and bank offices, upending a decades-old typology that no longer holds true for the contemporary networked, collaborative office.Item Modeling of non-ductile R/C flat-plate buildings subjected to seismic loading (earthquake loading)(1993) Luo, Yuanhui; Durrani, Ahmad J.Nonlinear dynamic analysis of non-ductile flat-plate buildings requires a suitable hysteretic model and an equivalent frame approach which appropriately models the lateral stiffness of the buildings. Based on the test results of non-ductile individual interior and exterior connections and two-bay slab-column subassemblies, hysteretic parameters related to stiffness degradation, strength deterioration and pinching of hysteretic loops are identified. The hysteretic model thus obtained is then incorporated into an equivalent frame analysis approach. The proposed equivalent frame approach is based on the equivalent beam concept which is calibrated to match the lateral stiffness and the moment-transfer strength of slab-column connections. Simulation of the load-drift response of the test subassemblies with the proposed analytical approach has good agreement with the measured response. Several slab-column buildings are designed as non-ductile systems and their response to typical earthquake loading is studied.Item Performance of reinforced concrete flat-slab buildings during Loma Prieta Earthquake(1992) AbouHashish, Amr Ahmed; Durrani, Ahmad J.This study is concerned with the performance of reinforced concrete flat-slab buildings during the Loma Prieta Earthquake. Three flat-slab buildings ranging from six to twenty-four stories were selected for investigation. Each building is analyzed using a number of different 3-D analytical models with a finite element program. Various models account for the change of stiffness of the slabs, columns, and shearwalls during the earthquake. The characteristic parameters determined from the analytical models are then compared with the identified characteristic parameters using the system identification techniques. Based on the comparison, a most appropriate model is selected which is then used in analyzing each building for lateral drift and base shear using the code defined lateral loads and also using the recorded ground acceleration. Based on the comparison of the recorded and calculated response, an estimate of the stiffness of the flat-slab is suggested which gives a better predication of the drift response under seismic loading. The comparison of the computed base shear from the dynamic analysis and the UBC seismic code shows the validity of the assumed distribution of the shear forces.Item Reliability analyses of the collapse and burst of elastic/plastic tubes(2001) Li, Guang; Nordgren, Ronald P.; Durrani, Ahmad J.The innovative methods proposed in this thesis provide effective and efficient solutions to the reliability problems of burst and collapse of tubes with random geometric imperfections under internal or external pressure. Steel tubes have broad applications in petroleum offshore engineering and must be designed to a safe but yet economical standard. The variation of imperfections from tube to tube necessitates a statistical characterization in which the burst and collapse pressures become random variables. In order to evaluate the burst and collapse pressure of a pipe with deterministic geometric imperfections, the finite element method is employed with a cylindrical shell element based on classical nonlinear shell theory. This element implements the return mapping algorithm for an elastic/plastic material and includes the effects of shell thinning and geometric imperfections. Incorporation of this finite element program into a reliability program developed for this study provides an effective numerical tool for the probabilistic analyses of the burst and collapse problems. For these analyses, the pipe thickness is modeled as an axially homogeneous and circumferentially inhomogeneous Gaussian random field based on measured data from two groups of pipes. Using the developed shell finite element program, Monte Carlo simulation (MCS) can be applied to the burst/collapse reliability problems. However, the enormous computational effort makes MCS infeasible except as a check for selected cases. Unfortunately, the system reliability method does not apply to the present problems because there are an infinite number of design points due to the special structure of the imperfections. Thus, a new approximate method is developed for the burst problem based on the correlations between the minimum thickness and burst pressure. The probability distribution of minimum thickness is obtained through an innovative homogenization procedure. Similarly, the collapse reliability problem is solved through introduction of a homogenized collapse function whose minimum correlates with the collapse pressure. The proposed reliability methods are applied to selected cases and verified by MCS. The effect of length on reliability in burst and collapse is investigated. Compared to MCS, the efficiency of the new methods makes them especially applicable to engineering problems, such as pipeline design and manufacturing quality control.Item Seismic resistance of fiber-reinforced slab-column connections(1991) Diaz, Alfonso J.; Durrani, Ahmad J.Three interior and three exterior fiber reinforced slab-column connections were subjected to gravity loads and then tested under lateral load simulating earthquake forces. Test results were compared to previous tests on non-fiber slab-column connections. Addition of steel fiber to the concrete matrix greatly increased the ductility and the energy dissipation capacity of all specimens. Fiber reinforcement also enhanced the shear capacity of interior connections. The failure mode switched from punching shear in interior connections with small amount or no fiber reinforcement to flexure failure in interior connections with higher fiber reinforcement ratios. Fiber reinforcement apparently did not improve the shear strength of exterior connections. The optimum amount of steel fiber found through the tests was between 50 and 100 pounds of fiber per cubic yard of concrete.Item Seismic resistance of slab-column connections in non-ductile flat-plate buildings(1993) Du, Yong; Durrani, Ahmad J.In order to determine the seismic response of existing reinforced concrete non-ductile flat-plate buildings, four reinforced concrete slab-column connection subassemblies designed for gravity load only were built at half-scale of prototype structure, and tested at Ryon laboratory of the Rice University. Each specimen had two exterior and one interior connections. The variables included the presence of spandrel beam, magnitude of gravity load, and reinforcing arrangement. The behavior of entire subassemblies and the individual connections under the cyclic loading was studied in terms of failure mode, stiffness, ductility, shear capacity, and moment transfer capacity in the two loading directions. Based on the test results, a procedure to predict the flexural and shear strengths of the interior and exterior connections is recommended. A hysterestic model for non-ductile slab-column connections is proposed. This model reflects the unsymmetrical moment transfer behavior of non-ductile connections. Furthermore, the model is incorporated in a non-linear dynamic analysis program and a typical flat-plate building is analyzed to demonstrate the application of the analytical model.Item Seismic response of connections in indeterminate flat-slab subassemblies(1990) Robertson, Ian Nicol; Durrani, Ahmad J.Recent earthquakes have shown the vulnerability of flat-slab structures to severe ground motion. The failure in such structures typically initiates at the slab-column connections in the form of a punching failure. This investigation was carried out to evaluate the adequacy of current procedures for the design of slab-column connections. The variables studied included the intensity of gravity loading, slab shear reinforcement at the column line, slab overhang and stiff edge beam at exterior connections, and the indeterminacy of the connection subassembly. Nine half scale slab-column subassemblies were tested under simulated earthquake loading. Seven of the subassemblies simulated a single floor of a two-bay flat-plate structure. Each subassembly consisted of one interior and two exterior slab-column connections. The remaining two specimens were individual interior and exterior connections. All specimens were subjected to the same predefined displacement routine which consisted of twenty cycles of incremental displacements increasing to a maximum of seven percent drift. Increased slab gravity load significantly reduced the drift capacity of both interior and exterior connections. To achieve a lateral drift level of 1.5 percent prior to failure, the ultimate direct shear on flat-plate connections must be limited to $V\sb{u} \leq C\sb{d}\sqrt{f\sb{c}\sp\prime}b\sb{o}d$, where $C\sb{d}$ = 2.0 for exterior connections and $C\sb{d}$ = 1.4 for interior connections. The ACI code design approach for interior connections was unconservative for higher gravity load levels. For the range of shear stress levels studied in these tests, the ACI Committee 352 recommendations that moment and shear be treated independently for design of exterior connections appears reasonable. The ultimate direct shear capacity of the exterior connections in this study was $V\sb{u} = 2\sqrt{f\sb{c}\sp\prime}b\sb{o}d$. Closed hoop stirrups enclosing the slab flexural reinforcement passing through the interior connection prevented punching shear failure and increased the ductility of the connection. A stiff edge beam or slab overhang at the exterior connections increased both the strength and ductility of these connections. The behavior of the combined specimens was similar to a summation of the individual connections especially at drift levels less than 1.5 percent.Item Seismic response of connections in indeterminate R/C frame subassemblies(1990) Zerbe, Hikmat Edward; Durrani, Ahmad J.The behavior of beam-to-column connections under earthquake-type loading has been studied in the past by testing isolated interior or exterior connections. In such tests, the beams are allowed to elongate freely when subjected to large deformation reversal. In a real building, however, the beams may be partially restrained against such elongation. The current design procedures which have been developed on the basis of tests on isolated connections, therefore, ignore the effects of continuity and beam elongation on the performance of connections. In this investigation, the behavior of connections was studied by testing indeterminate frame subassemblies under earthquake-type loading. Six half-scale multiple-connection subassemblies were tested. Each subassembly consisted of a two-bay frame isolated at the column mid-heights. Five single connection subassemblies were also treated to correlate the behavior of connections in multiple-connection subassemblies with the behavior of connections observed by testing isolated connections. Tests have shown that restriction to elongation of beams in indeterminate systems resulted in axial compression in beams which in turn had a significant effect on the performance of connections. The joint shear increased in both interior and exterior connections and the column-to-beam flexural strength ratio decreased. The energy dissipation was not affected by the continuity, but the lateral load resistance increased significantly. The stiffness degradation was more controlled and gradual in the indeterminate subassemblies compared to that observed in isolated connections. Based on the observed mechanism of lateral load resistance and the observed behavior of connections, a procedure is presented to account for the presence of axial compression in the main beams in the design of beam-to-column connections.Item Seismic response of slab-column connections with shear capitals(1991) Wey, Eric Hamilton; Durrani, Ahmad J.The punching shear strength of the slab usually governs the design of slab-column connections in regions of high seismicity. One method of increasing the shear capacity of the connection region is to increase the thickness of the slab using shear capitals. A shear capital is a thickened portion of the slab in the vicinity of the column used solely for improving the shear strength of the connection region. Three interior and three edge slab-column connections with different size shear capitals were tested under simulated earthquake type loading and compared to connections without shear capitals. Based upon the test results, the presence of a shear capital improves the strength and stiffness of a slab-column connection. A shear capital should be reinforced and have a sufficient length with respect to the depth of the slab when load reversals are expected.Item Shear strength of prestressed concrete t-beams with welded wire fabric as shear reinforcement(1985) Robertson, Ian Nicol; Durrani, Ahmad J.; Austin, Walter J.; Lutes, Loren D.In thin webbed prestressed concrete T-beams, the placement of conventional stirrups is difficult and time consuming. Welded wire fabric appears to provide a relatively economical alternative. In this study, the shear strength of prestressed T-beams reinforced with welded wire fabric as shear reinforcement is investigated. Thirteen large-scale bonded and unbonded prestressed T-beams were tested. The test variables included the type, amount and anchorage conditions of the shear reinforcement. These beams were tested under static third-point loading over a span of eleven feet. In all beams, shear failures occured along shallow diagonal tension cracks at loads in excess of the code predicted values. Anchorage of the welded wire fabric by means of two horizontal wires at top and bottom of the vertical web wires as recommended in the code performed well. However, the quality of the welded wire fabric was found to be critical for satisfactory performance.