Ali Abolmaali

End-plate connection moment-rotation relationship

Abstract A methodology, based on finite element modeling, is presented to analytically develop the moment-rotation relationship for a bolted steel end-plate connection. The methodology is demonstrated for a flush end-plate connection. Experimental testing of a few selected specimens was conducted to verify the finite element modeling and associated computer analysis procedure. The finite element model was used to conduct a parametric study to determined the effect of various geometric and force related variables on the prediction of maximum end-plate separation. Sufficient cases were then analyzed, which cover the variation of these variables within practical ranges. The analyses data collected were regressed to develop a predicton equation characterizing the general behavior of the connection.

Hysteresis behavior of semi-rigid double web angle steel connections

Abstract This study presents the cyclic behavior of two types of semi-rigid double web angle connections: bolted-bolted (angles bolted to the beam web and column flange) and welded-bolted (angles welded to beam web and bolted to column flange), with their bolts pretensioned to the proof load. Twenty test specimens were prepared and cyclic load was applied to each test specimen using load control at the beginning cycles, which was converted to displacement control in subsequent cycles upon yielding of angles or bolts materials. The moment–rotation hysteresis loops and the failure modes for all the test cases are presented. The failure modes for bolted-bolted test specimens, depending on angle thickness, were either excessive rotation or beam web bearing, and for the welded-bolted specimens were excessive rotation or bolt fracture. The stiffness, strength, and ductility of the tested connections are compared to those of flush end-plate moment connections reported in literature.

Sensitivity study of human crystalline lens accommodation

A nonlinear axisymmetric finite element method (FEM) analysis was employed to determine the critical geometric and material properties that affect human accommodation. In this model, commencing at zero, zonular traction on all lens profiles resulted in central lenticular surface steepening and peripheral surface flattening, with a simultaneous increase in central lens thickness and central optical power. An age-related decline in maximum zonular tension appears to be the most likely etiology for the decrease in accommodative amplitude with age.

A WEIGHTED RESIDUAL PARABOLIC ACCELERATION TIME INTEGRATION METHOD FOR PROBLEMS IN STRUCTURAL DYNAMICS

Abstract In the proposed method, the variation of displacement in each time step is assumed to be a fourth order polynomial in time and its five unknown coefficients are calculated based on: two initial conditions from the previous time step; satisfying the equation of motion at both ends of the time step; and the zero weighted residual within the time step. This method is non-dissipative and its dispersion is considerably less than in other popular methods. The stability of the method shows that the critical time step is more than twice of that for the linear acceleration method and its convergence is of fourth order.

Insights into the age-related decline in the amplitude of accommodation of the human lens using a non-linear finite-element model

Aim: To understand the effect of the geometric and material properties of the lens on the age-related decline in accommodative amplitude. Methods: Using a non-linear finite-element model, a parametric assessment was carried out to determine the effect of stiffness of the cortex, nucleus, capsule and zonules, and that of thickness of the capsule and lens, on the change in central optical power (COP) associated with zonular traction. Convergence was required for all solutions. Results: Increasing either capsular stiffness or capsular thickness was associated with an increase in the change in COP for any specific amount of zonular traction. Weakening the attachment between the capsule and its underlying cortex increased the magnitude of the change in COP. When the hardness of the total lens stroma, cortex or nucleus was increased, there was a reduction in the amount of change in COP associated with a fixed amount of zonular traction. Conclusions: Increasing lens hardness reduces accommodative amplitude; however, as hardness of the lens does not occur until after the fourth decade of life, the age-related decline in accommodative amplitude must be due to another mechanism. One explanation is a progressive decline in the magnitude of the maximum force exerted by the zonules with ageing.

Nonlinear Finite-Element Modeling Analysis of Soil-Pipe Interaction

AbstractThe effect of dynamic compaction forces is ignored in the analysis and design of underground structures. Several failure cases have been reported in which longitudinal cracks are observed during installation and compaction processes. Because, in the current specifications, compacting forces are not considered as design parameters, this study aims at determining the effect of dynamic compaction forces on RC pipes of different sizes. Thus, complete nonlinear three-dimensional finite-element models of pipe and soil are developed and verified against full-scale experimental testing. Particularly, crack initiation and propagation are modeled and predicted. Finally, the effects of dynamic forces are identified on the RC pipe.

Performance of Steel Fiber-Reinforced Concrete Pipes

This study presents the production and full-scale testing of steel fiber–reinforced concrete pipes (SFRCP) for the first time in the United States. Four reinforced concrete pipe (RCP) production sites in various geographical regions of the United States were selected for their diversity in production methods, and pipes with different fiber dosages were produced. The production sites selected were among the major RCP production facilities, whose equipment to manufacture pipes varied. The specific mix design for each production site was kept the same as that used for conventional RCPs to minimize the change in production culture. Pipes with diameters that ranged from 15 in. (400 mm) to 48 in. (1,200 mm) were produced with different fiber dosages. The SFRCP and control RCP specimens were instrumented and subjected to ASTM C497 three-edge-bearing, full-scale tests. The failure modes, strength, stiffness, and crack widths of the SFRCPs and RCPs were compared and reported.

Coupled Nonlinear Finite Element Analysis of Soil-Steel Pipe Structure Interaction

AbstractNumerical simulation of staged-construction modeling of large-diameter steel pressure pipes is accompanied by several complexities. Finite-element (FE) analysis was performed to simulate the behavior of buried steel pipes during staged-construction installation. The model deflections during the staged-construction process were verified with four different experimental soil box test results. The FE model and its associated analysis algorithm considered large deformation using total Lagrangian formulation. The material and contact nonlinear algorithms were also included in the analysis for both soil and steel pipe materials. The contact between each soil layer and soil-to-pipe was carefully implemented. Uniform thermal loading was applied to simulate the stresses induced by compaction forces on the pipe and trench walls. Finally, the vertical and lateral load-deformation plots obtained from the FE analysis results were compared with the full-scale experimental test results during the staged construc...

The relationship between accommodative amplitude and the ratio of central lens thickness to its equatorial diameter in vertebrate eyes

Aim: To determine the relationship between accommodative amplitude and central lens thickness/equatorial lens diameter (CLT/ELD) ratio in vertebrates. Methods: Midsagittal sections of lenses from fixed, post mortem eyes from 125 different vertebrate species were photographed. Their CLT/ELD ratios were correlated with independently published measurements of their accommodative amplitudes. Using the non-linear finite element method (FEM), the efficiency of zonular traction (the absolute change in central radius of curvature per unit force [|ΔCR|/F]) for model lenses with CLT/ELD ratios from 0.45 to 0.9 was determined. Results: Vertebrates with CLT/ELD ratios ⩽0.6 have high accommodative amplitudes. Zonular traction was found to be most efficient for those model lenses having CLT/ELD ratios ⩽0.6. Conclusions: Vertebrates with lenses that have CLT/ELD ratios ⩽0.6 – i.e. “long oval” shapes – have the greatest accommodative amplitudes; e.g. primates, diving birds and diurnal birds of prey. Vertebrates that have oval or spherical shaped lenses, like owls and most mammals, have low accommodative amplitudes. Zonular traction was found to be most efficient when applied to model lenses with CLT/ELD ratios ⩽0.6. The implications of these findings on the mechanism of accommodation are discussed.

Time-Dependent Behavior of Synthetic Fiber-Reinforced Concrete Pipes Under Long-Term Sustained Loading

This study presents the long-term behavior of synthetic fiber–reinforced concrete pipe (SYNFRCP) in actual field conditions. Conventional reinforced concrete pipe (RCP) was tested for comparison purposes. The research program was twofold. First, the short-term relationships between the applied loads and the deflections of SYNFRCP were obtained on the basis of the ASTM C497 three-edge bearing test. Second, the changes in the deformations of the buried RCPs and SYNFRCPs under sustained loading were monitored for up to 4,200 h. Two fiber dosages of 8 lb/yd3 (4.8 kg/m3) and 12 lb/yd3 (7.0 kg/m3) were used during the pipe production. Two 24-in. (600-mm) and two 36-in. (900-mm) pipes were buried in trenches with a sustained load of 1,350 lb/ft/ft (65 kN/m/m). The pipes were initially backfilled with native soil up to 2 ft (600 mm) and 4 ft (1,200 mm) over the top of the pipe and then backfilled with 14 ft of pea gravel above this to simulate the maximum fill height sustained by a Class 3 Wall B precast concrete pipe on the basis of ASTM C76. Two displacement transducers were installed from the crown to the invert at two sections along the length of each pipe. All buried pipes were precracked until the first visible crack was observed. The precracking was done to evaluate the long-term performance of SYNFRCP in which fibers are engaged after cracking. The strength, the crack width, and the change in the vertical deformation of the buried SYNFRCP and RCP are compared and presented in this paper.