Adel ElSafty

Business Strategy and Capital Allocation Optimization Model for Practitioners

Construction engineering companies usually provide a variety of services. To be competitive, companies have to organize their operations strategically based on market demands within the limitations of their own resources. Optimization of these resources is of vital importance for these companies. Historically, decisions on resource allocations to various construction market segments were made exclusively based on intuitive judgment. In previous literature, the proposed models on capital allocation place emphasis on formulating cash-flow forecasting and planning strategy on project level. However, existing technologies and established mathematical methods provide a sound base for quantitative analysis on company-level business strategy and capital allocation. This note proposes a linear programming model that can be conveniently applied by construction practitioners. The model incorporates the project cost structure and considers the business constraints such as bonding capacity and borrowing capital capac...

Statistical analysis and theoretical predictions of the tensile-strength retention of glass fiber-reinforced polymer bars based on resin type

This paper presents experimental investigation, statistical analysis, and theoretical predictions of tensile-strength retention of glass fiber-reinforced polymer bars, made with vinyl-ester, polyester, or epoxy resins. The durability of glass fiber-reinforced polymer bars was evaluated as a function of time of immersion in alkaline solution. The aging of the three glass fiber-reinforced polymer bar types consisted of immersion glass fiber-reinforced polymer bar samples in an alkaline solution (up to 5000 h) at different elevated exposure temperatures. Subsequently, the physical and tensile properties of the unconditioned bars were compared with that of the conditioned bars to assess the durability performance of the glass fiber-reinforced polymer bars. Microstructure of all of the glass fiber-reinforced polymer bar types was investigated with scanning electron microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy for both the conditioned and unconditioned cases, to qualitatively explain the experimental results and to assess changes and/or degradation in the glass fiber-reinforced polymer bars. In addition, the long-term performance of glass fiber-reinforced polymer bars was assessed considering the effect of service years, environmental humidity, and seasonal temperature fluctuations. The test results showed that the tensile strength of the glass fiber-reinforced polymer bars was affected by increased immersion time at higher temperatures and the reduction in tensile strength was statistically significantly dependent on the type of resin system. The prediction approach of the glass fiber-reinforced polymer bars based on the environmental reduction factor (CE) after 200 years indicated that the CE values for vinyl-ester, epoxy, and polyester glass fiber-reinforced polymer bars can be conservatively recommended to 0.81, 0.75, and 0.71, respectively, for a moisture-saturated environment (relative humidity = 100%) and at 30℃. The polyester glass fiber-reinforced polymer bars experienced greater debonding at the fiber–resin interface than the vinyl-ester and epoxy glass fiber-reinforced polymer bars.

Limiting Early-Age Cracking in Concrete Bridge Decks

Early-age bridge-deck cracking is a major problem affecting the durability of U.S. bridges. Many factors can cause early-age bridge-deck cracking including change in temperature, hydration, plastic shrinkage, autogenous shrinkage, and drying shrinkage. The presence of cracking may increase the effect of freeze and thaw cycles and may lead to corrosion of reinforcement, which may result in deterioration of the entire bridge. It is crucial to investigate the issue of early-age cracking in bridge decks to provide solutions to improve the safety of U.S. bridges. This research examines the use of different sealing materials to seal the developed cracks while the performance criteria can be achieved. An analytical study was performed to study the importance of major parameters that may affect the transverse deck cracking, such as concrete strength, shrinkage, thermal effect, load patterns, load magnitude, span length, number of spans, and continuity. A finite-element model was developed to investigate the factors affecting tensile stresses and crack tendency. Also, a tool was developed to predict the likelihood and initiation of early-age cracking in bridge decks. The outcomes of this study identify suitable sealant materials and identify a set of recommendations to limit the cracking problem and, hence, resulting in a longer service life to bridges.

Effect of applied sustained load and severe environments on durability performance of carbon-fiber composite cables:

The research work reported in this paper involves investigation of the mechanical and durability performance of unstressed and stressed Tokyo Rope carbon-fiber composite cables for prestressing applications. This research is critical in order to establish the critical (allowable) stress and safety factors for the use of carbon-fiber composite cable tendons for prestressed precast-concrete members. The carbon-fiber composite cable specimens were exposed to simultaneous high alkali environment and sustained loading at different elevated exposure temperatures (22℃ and 60℃) for 3000, 5000, and 7000 h. The high alkali environment (12.8 pH) simulated the concrete pore solution and the elevated temperature was used to accelerate the aging process. The applied sustained stress on the carbon-fiber composite cable strands was equivalent to 40% and 65% of their guaranteed tensile strength. This was achieved through testing 171 carbon-fiber composite cable specimens subjected to stress levels of 0%, 40%, and 65% of their guaranteed strength, under tensile load. Also, 136 carbon-fiber composite cable specimens were tested to investigate the transverse shear strength. In addition, the durability characteristics of the constituent materials of the carbon-fiber composite cable strands were assessed to understand the long-term behavior of these materials. The results showed the effect of sustained stress on the degradation of carbon-fiber composite cable strands. Under sustained stress of 40% and 65%, the reductions in tensile strength were 10.6% and 12.3%, respectively. Scanning electron microscope results on epoxy resin indicated that no degradation is detected since the surface remains smooth without any pitting or loose material.

Effects of Global Climate Change on Building Energy Consumption and Its Implications in Florida

ABSTRACT Many studies have investigated the impact of global warming on energy consumption. In this study, the morphing method and EnergyPlus (E+) software were used to investigate the impact of climate change on commercial building energy use under the A2 medium-CO2. emission scenario. The study simulated electricity and gas consumption of nine types of commercial buildings in eight cities, representing three climate zones in Florida. The nine types of commercial buildings included apartments, hotels, offices, and schools. The energy simulation results showed the future trends of growth and reduction in electricity and gas consumption for cooling and heating in TMY2 (TMY3), 2020, 2050, and 2080 in the eight selected cities. In general, gas and electricity demands for heating are projected to decrease, and electricity demand for cooling increases, at different rates in various areas of Florida. The study provides guidance for policy‐makers and utility companies as they craft their response to climate change in various regions of Florida.

Repair of damaged steel beams composite with concrete deck using carbon fiber reinforced polymers (CFRP)

S engineers are often involved in projects to strengthen deficient structures as a feasible alternative to cost-prohibitive full replacement of the structure. The use of composite materials to strengthen existing concrete structures by externally bonding thin laminates or strips is mature enough that design codes and guidelines are available for flexural, shear, and axial strengthening applications. Researchers have also investigated strengthening steel structures using composite material, however, the field is not as mature as it is for concrete applications. This paper presents a new strengthening technique where pultruded GFRP sections are bonded to shear deficient regions to enhance the local buckling resistance of the thin walled steel structures. The technique, referred to as strengthening-by-stiffening or SBS, was developed at Louisiana State University. An experimental program was designed to study the effect of FRP stiffener configuration on the efficiency of SBS. Different orientations, web slenderness values and aspect ratios were tested monotonically up to failure. The ultimate shear capacities beams were enhanced by a minimum of 30% when one stiffener was used on a beam with a square panel and a maximum of 56%. Post yielding behavior including the transition from a tension field to sway-frame load path will also be discussed.C walling system consisting of two skins of profiled steel sheeting and an infill of concrete is novel form of construction. Such walling system has great potential to be used as gravity and lateral load resisting elements in buildings. The strength, stiffness, ductility and energy absorbing capacity of composite walls subjected to axial, monotonic/cyclic shear and impact loadings will be described based on comprehensive experimental and theoretical investigations. The fire durability of the walls subjected to high temperatures will also be presented based on residual strength/stiffness/energy absorption capacity. The innovative feature of such walls is the use of new engineered high performance concretes (HPCs) with high strength, high ductility (strain hardening capacity) and micro-cracking characteristics developed at Ryerson University for the last few years. Such HPC composite walls have shown superior performance compared to those made with traditional concrete in terms of strength, ductility, energy absorbing capacity and durability as well as post-impact strength/stiffness/ energy absorbing capacity. Analytical models/design equations for the load resistance of composite walls are developed and their performance validated through experimental and finite element modeling.T task at the present study was the verification of the current methods used in a conventional manner so as to estimate the behavior of a tunnel against ground motion but also the investigation and suggestion of additional methods. To accomplish this objective, the study analyzes a real project that had been designed by the engineering team of Geodata. Moreover there is a review of what has already been applied to the case (pseudo-static methods) and in parallel there is a consideration of various other existent procedures: analytical, dynamic time-history and a different numerical model again in pseudo-static condition. The time-history method is highlighted in particular as it is a rigorous scheme that needs prudent consideration. In the end, the comparison brought out both advantages and drawbacks but as well as the contrasts of the distinct proceedings and made the associated proposal for future performance issues. Creating a model for a pseudo-static approach has a simplicity that makes it advisable as the primary way to characterize the situation. On the other hand, it is the only way among all those that were described at the study and can exist on its own. The model itself is capable of enclosing sufficient results provided that the configuration guarantees a reliable representation of the surrounding mass conditions (in the present case, the project adopted pure material homogeneity and a detailed grid around the tunnel). Shear deformation is the dominant value that plays the role to define the level of the response and therefore the dynamic analysis was also a tool to detect the relative strain levels. Even so, a thorough search among past ground motion scenarios brings the suitable records (the key parameter here is the PGA of the region) that can more or less set the stress-strain framework to strengthen the reliability of the numerical model. The use of time-history (dynamic) analysis requires a suitable record selection (three or more) and a number of accompanying checks. The record time-histories must be compatible to the site response spectrum and were scaled to the relevant PGA. Further checks have to do with the frequency propagation ability offered by the model but also with the energy content of the input. Even the damping issue is considered in more than one ways. Consequently, this method turns out to be a useful, representative and exceptional tool as it is the only one that inserts dynamic loading. The basic topic is the interaction and the coexistence of the dynamic analysis with any simplified numerical approach. Such a combination is to be further examined at a large group of deep elements. This study demonstrates that, the two methods, if put together, can set the analyses to the same strain levels and consequently the correlation between them will be considered much more valid so as to evaluate the seismic response of the structure.

Optimum CFRP Configuration to Efficiently Repair Laterally Damaged, Simply Supported Rectangular Reinforced Concrete Beams

This research investigated flexural behavior of repaired RC beams that experienced simulated lateral damage to replicate vehicle impact/collision. The experimental program included the testing of 34 RC beams, which were laterally damaged and then repaired using carbon-fiber-reinforced polymer (CFRP) fabrics. The damaged beams were repaired using various levels of strengthening (number of CFRP soffit layers) and multiple configurations of anchoring CFRP U-wrapping. Specific attention was paid to understanding the effects of intermediate U-wrapping on strains developed in the longitudinal soffit laminates and the beams’ ultimate capacity. Other details for the flexural repair system, such as end-peeling previsions, were also addressed. The test results indicated that CFRP repairs have the ability to restore and enhance the capacity of damaged RC beams by up to 353%. The results also suggest an optimum range for spacing intermediate U-wrappings to suppress strains felt by longitudinal soffit laminates, thereby mitigating premature debonding failures. Design considerations and recommendations for optimum CFRP configuration, level of strengthening, and application details for repairing laterally damaged RC beams are proposed.

Assessment of Carbon Fiber Reinforced Polymer Repair for Laterally Damaged Prestressed Concrete Girders

This paper presents an investigation of the most efficient configuration of carbon fiber reinforced polymers (CFRP) for repairing laterally damaged prestressed concrete (PS) bridge girders. The flexural behavior of 10 half-scale AASHTO type II 20-ft-long PS girders is presented in this paper. Lateral damage due to vehicle collision impact was simulated by sawing through the concrete of the bottom flange and slicing through one of the prestressing strands. The damaged concrete was repaired, and different CFRP repair configurations (longitudinal soffit strips and U-wrapping) were applied. Both the control and repaired PS girders were tested in flexure until failure using a four-point loading setup. Measurements of the applied load, the deflection at five different locations, strains along the cross-section height at mid-span, and multiple strains longitudinally along the bottom soffit were recorded. We also compared the performance of girders with full wrapping of CFRP to that of girders with longitudinal CFRP strips applied to the bottom of girders combined with discrete, spaced U-wrapping strips. Conclusions are drawn regarding the most efficient CFRP design configuration for avoiding CFRP debonding and undesired failure modes.