Ayman Mosallam

Study on the Mechanical Properties of Different Silkworm Silk Fibers

Mechanical properties of Bombyx mori, twisted B. mori, and Tussah silk fibers were investigated. Their ultimate tensile strength, elongation at break, and Young’s modulus were examined by performing a uniaxial tensile test on a single fiber. Scanning electron microscopy was used to observe the morphology of two different types of silk fiber, and to measure their apparent diameters from which the cross-sectional area of the silk fiber for stress-strain analysis can be determined. Based on experimental results obtained, it was found that Tussah silk fiber has a relatively high extensibility as compared to B. mori silk fiber and other natural fibers. Weibull analysis was also used to quantify tensile strength reproducibility of the silk fiber. Both single and twisted B. mori silk fibers have a better reproducibility of tensile properties than Tussah silk fiber.

Composite army bridges under fatigue cyclic loading

Military composite bridges offer many unique advantages to the army—for example their high strength-to-weight ratio and superior corrosion and fatigue resistance properties—compared to current steel and aluminum bridges. This paper presents the results of part of a comprehensive, on-going research program sponsored by the US Army to develop innovative field repair techniques for military composite bridges. The virtual tests were performed on the composite treadway under four different loading cases: (i) maximum shear static loading case, (ii) maximum bending static loading case, (iii) fatigue progressive failure analysis for the moving load case, and (iv) fatigue progressive failure analysis for the maximum flexural loading case. Results of virtual testing and progressive failure analysis (PFA) simulation conducted on a composite army bridge (CAB) prototype demonstrated a good match with the full-scale laboratory test results conducted in an earlier study. For instance, the variation between the maximum deflections predicted by the GENOA simulation for the maximum shear and those obtained from the full-scale tests was only 3.2%. In addition, the location and type of damages at the ultimate load were very close to those obtained from the full-scale laboratory tests.

A comparative study on static and dynamic responses of FRP composite and steel suspension bridges

Fiber reinforced polymer (FRP) composites offer many attractive and unique features for existing and new bridges. Among these features are light weight, high stiffness-to-weight and strength-to-weight ratios, damping capabilities, and high resistance to environmental degradation when properly designed and installed. This article presents a pilot numerical study aiming at evaluating the feasibility of using FRP composites in suspension bridge applications. This was accomplished by comparing the response of two identical long-span suspension bridges, one constructed from FRP composite and the other made of steel under static and dynamic loadings using FEM. The numerical results indicated that the responses of the two bridges are different and that the response values obtained for the steel bridge are relatively large compared to the composite bridge. Despite different mode sequences of the two bridge models, the dynamic analysis results indicated that both bridge models have similar mode shapes. As a result of lower self-weight of the FRP composite bridge model, the frequencies of the FRP composite bridge model are larger than those of the steel bridge model.

Wireless MEMS - Sensor Networks for Monitoring and Condition Assessment of Lifeline Systems

This paper summarizes and combines the recent papers by two of the authors and demonstrates a potential use of a sensor-based real-time monitoring and condition assessment system for urban lifeline infrastructure. Rapid detection of damage caused by natural and manmade hazards enables an efficient and effective emergency response minimizing human and property losses as well as societal disruption. In this paper, using a small scale model of water pipeline network as an example, we demonstrate a monitoring system consisting of a wireless network of power-efficient sensors for a rapid identification of the extent and location of pipe damage immediately after a disastrous event. In this particular example, we take advantage of sharp transient change in the water head due to the damage. The result suggests that a simple inverse analysis can locate the damage in a pipe segment between two neighboring sensors among the pervasively installed along a pipeline at which the absolute values of water head are observed to be local maxima. Separate experiment and analysis show that the sharp transient change in water head in the pipe flow induces a correspondingly sharp change in the acceleration of pipe vibration on the pipe surface. This fact is conventionally used for damage identification in this study.

Buckling and ultimate failure of thin-walled pultruded composite columns

This paper presents the results of an investigation on the buckling behavior of concentrically loaded thin–walled pultruded fiber reinforced polymer (PFRP) composite columns. Both open- and closed-web columns were evaluated. Finite element (FE) analysis and theoretical predictions are presented and correlated with experimental data. Good agreement between theoretical, analytical and experimental results was achieved. The paper also presents design guidelines to determine the bending stiffness and the critical buckling load for pultruded composite columns. In addition, a discussion on the axial strength of unidirectional PFRP columns and identification of different modes of failure are presented.

COMPOSITES: CONSTRUCTION MATERIALS FOR THE NEW ERA

With over fifty years of excellent performance records in the aerospace industry, fiberreinforced-polymer (FRP) composites have been introduced with confidence to the construction industry. These high-performance materials have been accepted by the civil engineers and have been utilized in different construction applications such as repair and rehabilitation of existing structures as well as in new construction applications. This paper provides an overview of the successful and unique applications of FRP composites in construction. The paper also presents a state-of-the-art review on code and specification developments in the USA and worldwide.

Hygrothermal aging effects on axial behaviour of pultruded web–flange junctions and adhesively bonded build-up bridge members

Premature local failure of web/flange junctions of the majority of unstiffened commercially produced pultruded fiber-reinforced polymer composites profiles is inescapable due to lack of fiber continuity at the resin-dominated junction zones. This paper focuses on evaluating both short- and long-term behavior of such junctions when subjected to axial tensile stresses. In this study, the axial mechanical behavior of web/flange junctions of pultruded bridge deck components before and after hygrothermal aging effect is investigated. In the experimental phase, axial tensile tests were performed on six different types of pultruded web–flange junctions to assess axial characteristics of each web/flange junction type. In order to evaluate the hygrothermal behavior of such junctions, axial tensile tests were conducted on web/flange junction specimens that were exposed to both fresh water and artificial seawater environments at temperatures of 40℃, 60℃, and 80℃. Several controlling parameters affecting both strength and stiffness of pultruded fiber-reinforced polymer junctions were identified and discussed that include: (i) Junctions web and flange thicknesses, (ii) fillet radius, and (iii) variation of hygrothermal exposure environments. Results of this study indicated that the axial tensile capacity of a pultruded profiles is increased as the thickness of both web and flange increases. Also, it was found that the larger fillet radius of the pultruded fiber-reinforced polymer profile may contribute to a larger axial tensile capacity of pultruded profiles. However, due to variable size and geometry of the resin-rich junction zones and the common manufacturing defects in the form of folded fabric and other fibers misalignment effects, it is difficult to generalize the preceding results. Experimental results also showed that the degradation of web/flange junctions axial tensile strength increases when junctions are exposed to higher temperatures. Also, it was found that the axial tensile characteristics for junctions specimens exposed to freshwater environment are slightly different than those that were exposed to artificial seawater environments.

Incorporating global search capability of a genetic algorithm into neural computing to model seismic records and soil test data

Abstract In this study, a genetic algorithm with global searching capability was incorporated into a neural network calculating process to obtain a highly reliable model for predicting peak ground acceleration, which is the key element in evaluating earthquake response and in establishing a seismic design standard. In addition to three seismic parameters (i.e. local magnitude, focal distance, and epicentre depth), this study included two geological conditions (i.e. standard penetration test value and shear-wave velocity) in the input to reflect the site response adequately. Based on the earthquake records and soil test data from 86 checking stations, within 24 seismic subdivision zones in the Taiwan area, the computational results show that using a combination of a neural network and genetic algorithm can achieve a higher performance compared with solely using a neural network model. Furthermore, a weight-based model was developed for predicting peak ground acceleration at an unmonitored site to represent each subdivision zone. The results show that three subdivision zones have higher horizontal peak ground accelerations than the seismic design value as required in the building code. The obtained information might be helpful in relevant engineering applications for the studied region, and the proposed method for treating this type of nonlinear seismic data might be applicable in other areas of interest worldwide.

DEVELOPMENT OF A DIAGNOSTIC/PROGNOSTIC SYSTEM (DPS) FOR MONITORING THE PERFORMANCE OF REPAIRED COMPOSITE MILITARY BRIDGES

Composite bridges offer many advantages compared to current steel and aluminum bridges including their lightweight and superior corrosion resistance properties. This paper presents the results of a comprehensive on-going research program to develop innovative field repair techniques for composite bridges. In this study, an innovative Diagnostic/Prognostic System (DPS) for monitoring the performance and reliability of a smart repair kit (SRK) for composite military bridges has been developed. The DPS system is founded on three technologies, namely; optical fiber sensing, remote data transmission and virtual testing. In developing this system, both laboratory and virtual tests simulating the different potential damage scenarios. In order to minimize the number of expensive full-scale tests, virtual testing technique using an advanced progressive failure simulator code (GENOA) was utilized. The results of the pre-simulated damage scenarios are stored in a secure database. Different composite patches with optical fiber sensors are being developed for different damage types. These smart patches act as health-monitoring devices for different parts of the composite bridge, especially areas surrounding the repaired portions of the bridge. In the event of local damage such as debonding of any patch due to excessive loading or lower application quality, for example, the stress distribution will change.

Window opening effects on structural behavior of historical masonry Fatih Mosque

ABSTRACT Structural walls of old historical structures are either blind or have openings for functional requirements. It is well known that in and out of plane responses of structural walls are affected by the size, locations, and arrangements of such openings. The purpose of this investigation is to study the window opening effects on static and seismic behaviors of historical masonry old mosques. Fatih Mosque, which was converted from a church, constructed in 914 in Trabzon, Turkey, is selected for this purpose. The mosque is being restored. Structural exterior walls of the mosque were made using stone and mortar materials. When the plaster on the walls was removed during the restoration, 12 window openings were found as blind on the exterior structural walls of the mosque. Within the scope of restoration works, it is aimed to open such blind windows. In order to investigate the effects of the window openings on the structural behavior of the mosque, 3D solid and finite elements models of the mosque with and without window openings are initially developed. The experimental dynamic characteristics such as frequency, damping ratio, and mode shapes of the current situation of the mosque, where some windows openings are blind, are determined using Ambient Vibration Testing. Then, the finite element model of the current situation of the mosque is updated using the experimental dynamic characteristics. The static and seismic time history analyses of the updated finite element model with and without window openings are carried out. Structural behaviors of the mosque with and without window openings are compared considering displacement and stress propagations.