Sherif A. Mourad

Computer-Aided Assessment of Progressive Collapse of Reinforced Concrete Structures according to GSA Code

A building is subjected to progressive collapse when a primary vertical structural element fails, resulting in the failure of adjoining structural elements, which cause further structural failure, leading eventually to partial or total collapse of the structure. The failure of a primary vertical support might occur because of extreme loadings such as a bomb explosion in a terrorist attack, a car colliding with supports in a parking garage, an accidental explosion of explosive materials, or a severe earthquake. Different design codes address the progressive collapse of structures attributable to the sudden loss of a main vertical support such as the General Services Administration (GSA) code and the Unified Facilities Criteria (UFC). The alternative path method (APM) is the main analysis method for evaluating the hazard of progressive collapse in the two codes. The APM requires that the structure be capable of bridging over a missing structural element, with the resulting extent of damage being localized. In the current study, a progressive collapse assessment according to the GSA code is carried out for a typical ten-story RC-framed structure. The structure is designed according to the building code requirements for structural concrete. Fully nonlinear dynamic analysis for the structure is carried out using the applied-element method (AEM). According to the GSA code, a primary vertical structural element is removed, and the collapse area is investigated. The investigated cases include the removal of a corner column, an edge column, an edge shear wall, internal columns, an internal shear wall, and a corner shear wall. The numerical analysis showed that, for an economic design, the analysis should consider slabs and cannot be simplified into a two- or three-dimensional frame analysis. Neglecting the slabs in the progressive collapse analysis is a very conservative approach that may lead to uneconomic design. The RC structures designed according to American Concrete Institute guidelines met the GSA limits and were found to have a low potential for progressive collapse.

Observations from the 12 October 1992 Dahshour earthquake in Egypt

An earthquake of local magnitude 5.3 (duration magnitudeMd) on the Richter Scale occurred at Dahshour, 18 km south of Cairo, Egypt, on Monday, 12 October 1992 at 3:09 pm (local time). Numerous aftershocks followed the main event during the following weeks with magnitude up to 4.3. The earthquake occurred in an area that has had no recent seismic activity, and affected many cities in Egypt. Many buildings and monuments were severely damaged or collapsed. Modern concrete skeletal structures suffered minor nonstructural damage. Earthquake physical damage was estimated at about one billion U.S. Dollars. The severity of the damage was mainly due to poor construction materials and detailing, aging, inferior workmanship, and inadequate maintenance. Egypt was generally considered to be an area of moderate seismic activity. In 1989, earthquake provisions were first introduced in the Egyptian Code of Practice for Reinforced Concrete Structures only. The earthquake clearly showed the urgent need for an assessment and rehabilitation program to mitigate seismic risk hazard in existing structures. In addition, future development planning, and earthquake preparedness strategies should implement lessons learned from the event. In this paper, an overview discussion about the observations from the 12 October earthquake is presented.

Behavior of concentrically loaded CFT braces connections

Concrete filled tubes (CFTs) composite columns have many economical and esthetic advantages, but the behavior of their connections is complicated. Through this study, it is aimed to investigate the performance and behavior of different connection configurations between concrete filled steel tube columns and bracing diagonals through an experimental program. The study included 12 connection subassemblies consisting of a fixed length steel tube and gusset plate connected to the tube end with different details tested under half cyclic loading. A notable effect was observed on the behavior of the connections due to its detailing changes with respect to capacity, failure mode, ductility, and stress distribution.

Alternate Path Method Analysis of RC Structures Using Applied Element Method

Recent research using the Applied Element Method (AEM) shows that the method is efficient in modeling progressive collapse analysis of structures. Recent research on progressive collapse design of structures based on the UFC code shows it can be used in optimizing the design for structures for which the alternate path method is required. This paper demonstrates the efficiency of the use of AEM in progressive collapse analysis of reinforced concrete structures by comparison to results of published experimental tests. A case study based on a typical seven-story reinforced concrete frame commercial building is used to demonstrate the advantages of using the alternate path method in progressive collapse design of concrete structures even for the cases where the code permits the use of the tie force method. The contribution of infill walls in resisting progressive collapse is also studied.

Experimental study of prequalified status of flush end plate connections

Abstract Seismic design of steel structures is an essential part of the design process. Egyptian loading code development process continues in a high rate to catch up with emerging new concepts and standards. Steel design codes (ASD and LRFD) are not developing in the same speed, which prevents the full utilization and application of loading code. The above reason leads to the need for evaluating flush end plate connections from prequalification point of view according to international standards. Due to the lack of sufficient experimental data on flush end-plate connections, an experimental program was conducted to investigate this topic. Six flush end-plate samples were designed according to the Egyptian code for steel construction (ECP205 ASD) using different beam and column sections, bolt diameters and grades. A cyclic loading pattern defined by international standards was used in the testing process, and the performance was evaluated accordingly. Evaluation of M–Φ curves showed that in some cases flush end plate connections satisfy the strict requirements for prequalification. However, beam sections having limited depth fail to achieve prequalification criteria for the connections. Reduced web may be used to enhance the connection status and is investigated in one of the samples to evaluate its impact on connection performance and the failure mode. The proposed staggered hole configuration showed a promising performance.

Imperfection Modeling Using Finite Element Approach with Particular Discretization

AbstractThe research reported in this paper presents an attempt to improve the modeling of imperfections in steel structures using a finite-element approach with particular discretization. This approach, termed the modified finite-element beta method (MFEM-β), is an improvement of a finite-element scheme that can handle displacement discontinuity. In MFEM-β, a multilinear isotropic hardening model is implemented, a random imperfection procedure is proposed, and a modified failure treatment is adopted. The paper reviews the progression of the original scheme, presents the proposed imperfection procedure, and uses the results of two experimental tests to demonstrate the imperfection effect on the failure of a uniaxailly elongated steel plate and to validate MFEM-β. The proposed method simulates the boundary and internal imperfections, and controls the intensity and distribution of the imperfections using six input parameters to randomly assign the imperfections to the numerical model. Showing an advance ove...

SWOOP: An adjustable global optimization technique

Abstract Optimization is the process of obtaining the best result under given circumstances and in its broadest sense; optimization can be applied to solve any engineering problem. In many practical applications, the objective function contains, besides the global minimum, several local minima. Implementing local optimization algorithms to functions that contain multiple local minima within the search space results in problem instability. Unfortunately, the distinction between the concepts of local and global optimization is frequently overlooked by researchers although a huge amount of work has been done in this field due to the cumbersome of implementing a global optimization technique. A recent technique for global optimization was developed under the name of Coupled Local Minimizers (CLM) in which the local minimizers exchange information with each other resulting into a cooperative search mechanism. This technique was comprehensively discussed in the realm of finite element model updating and many challenges were illustrated that hinder the practical implementation of the technique. In this paper, the authors present a modified version of the CLM technique under the name of SWOOP in some of the drawbacks the CLM are mitigated, and then added a perusal part to the technique by plotting a synthesized response surface of the function to guide the optimization process. The proposed SWOOP technique is tested for various function types and its superior performance was validated.