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Sherif El-Tawil, PhD, PE

Professor and Associate Chair
Department of Civil & Environmental Engineering | The University of Michigan

Completed Research Projects

Title: Development, Characterization and Applications of Non Proprietary Ultra High Performance Concretes for Highway Bridges
Sponsor: Michigan Department of Transportation (MDOT)
Project Duration: 2012-2016

Synopsis: Ultra-high performance concrete (UHPC) is a new class of cementitious materials that have exceptional mechanical and durability characteristics. UHPC is commercially available. However, its cost for construction of highway structures is prohibitive. Based on an extensive testing program, a new family of non-proprietary UHPC materials with excellent characteristics in compression and tension, as well as exceptional resistance to freeze-thaw and chloride ion penetration was developed. The most cost effective of these deviates from traditional UHPC mixtures in that it uses a 50:50 mix of Portland Type I and Ground Granulated Blast-Furnace Slag (GGBS) as a binder, lacks any silica powder (inert filler) and requires no post-placement treatment. The use of GGBS improves the material's ‘greenness' making it a more sustainable cementitious product. Specifications for making the new UHPC were proposed. The developed UHPC blend was then used to conduct a comprehensive study on bond between UHPC and deformed steel bars to facilitate and enable future structural applications. Bond pull out tests showed the developed UHPC requires significantly reduced development lengths in order to attain steel bar yield compared to traditional concrete. Models to characterize the bond strength were proposed and a UHPC joint consisting of two pre-cast bridge deck elements was developed and tested at full scale. It was shown that a 6” (150 mm) joint made of the developed UHPC was sufficient to successfully transfer loading between the decks.

Title: Framework for Quantifying Structural Robustness through Modeling and Simulation
Sponsor: National Science Foundation (NSF)
Project Duration: 2009-2013

Synopsis: Robustness is the ability of a structural system to resist progressive collapse. While research on evaluating structural robustness has been ongoing for a while, many critical questions still remain unanswered. In particular, it is not yet clear what sources of resistance are mobilized during collapse and whether structural robustness can be quantified. To address these questions, the study investigated the robustness of seismically designed steel moment frame buildings using 3-D nonlinear models that were comprehensively validated against experimental data. Simulations studies were then conducted using these models to gain insight into the sources of collapse resistance of the prototype buildings, focusing in particular on the role of composite action between the slab and underlying steel beams and slab membrane action. Emphasis was also placed on identifying the how various types and levels of modeling approximations influenced the computed responses.

Title: Project IBORC: Interaction between Building and Occupant Responses during Collapse
Sponsor: National Science Foundation (NSF)
Project Duration: 2008-2012

Synopsis: The objective of this project is to conduct a multidisciplinary investigation at the intersection of structural engineering, social science, and computer science of how people respond to emergencies. Computational simulation models were developed to represent building collapse (the hazard) and human egress (the response). Agent Based Models (ABMs) were used to model human behavior. ABM is a computational simulation methodology used to build an artificial society. The simulation is populated with computer-driven agents that have their own characteristics, are different from others, and are adaptive and capable of interacting with each other and with their environment. The interactions of interdependent agents generate complex systems, usually understood as emergence, that otherwise could not be obtained through the addition of the parts. ABM provides information relevant to the conduct of experiments for which real-world data collection would be unethical, impractical, or prohibitively expensive, hence its use for the proposed work. A new ABM was developed in this project in collaboration with the Disaster Research Center at the University of Delaware. The newly developed model is one of the first to incorporate group social behavior. Most existing models to date are based upon the "sole actor" model, where every person makes selfish evacuation decisions based on self-preservation. Current social science theories have disproved the so-called panic egress mode, and indicate that people interact socially during evacuation. Agents embedded within models of collapsing buildings were used to investigate how people response during extreme situations.

Title: Characterizing High-Strain-Rate Response of Cementitious Composites Using a Novel Strain-Energy-Based Impact Test System
Sponsor: National Science Foundation (NSF)
Project Duration: 2008-2011

Synopsis: A novel test system was proposed for characterizing the high-strain-rate response of materials. The new method exploits the internal strain energy accumulated in an elastic bar to impart a high speed, high energy pulse onto a specimen. The new test system overcomes the combined limitations of traditional impact test setups and enables high quality impact testing in a scalable, cheap, compact, fast and safe manner. Another critical advantage is the ability to test with a small set-up, relatively large size specimens, which permits tests that more truly represent the behavior of non-homogenous building materials. Fundamental research was conducted to optimize and explore the capabilities of the new system.

Title: Rapid Post-Disaster Reconnaissance for Building Damage Using Augmented Situational Visualization and Simulation Technology
Sponsor: National Science Foundation (NSF)
Project Duration: 2007-2011

Synopsis: This project investigated methods for using Augmented Reality (AR) to evaluate earthquake-induced building damage. Previously stored building information was superimposed onto the view of a real structure in AR and structural damage could be quantified by measuring and interpreting key differences between the real and augmented views. Proof-of-concept experiments were performed to demonstrate the feasibility of the proposed technology. Reduced computational models were also developed that could run rapidly enough to be used for in-situ evaluations of structural response.

Title: NEESR-SG: Innovative Applications of Damage Tolerant Fiber-Reinforced Cementitious Materials for New Earthquake-Resistant Structural Systems and Retrofit of Existing Structures
Sponsor: National Science Foundation (NSF)
Project Duration: 2005-2010

Synopsis: This project focused on developing a better understanding of the inelastic cyclic response of structures comprised of high performance fiber reinforced cementitious composites (HPFRCCs). HPFRCCs are a class of materials that are ductile in tension, do not spall in compression, behave like a confined concrete, and capable of providing confinement to normal reinforcement. In addition to enhancing confinement and flexural behavior in plastic hinging regions, HPFRCC materials are capable of providing ductility and energy dissipation capabilities to shear critical members that are normally a difficult design issue for RC structures. The project contained several phases: development of a commercially viable HPFRCC, testing of components and system, development of novel computational tools and simulation of system response to seismic excitation.

Title: Improving USAR Preparedness using Simulation Technology
Sponsor: National Science Foundation (NSF)
Project Duration: 2005-2008

Synopsis: When a building collapses due to a catastrophic event, stable voids are inevitably formed in the rubble pile. These voids occur as a result of falling structural and nonstructural elements that interact together in a favorable manner to create spaces in which victims may find shelter. Since as many as one third of all building collapse victims that are rescued are found in such spaces, the primary objective of this research was to use state-of-the-art finite element simulations to investigate how, and under what conditions, they are formed. The project employed detailed finite element simulations coupled with virtual reality visualization techniques.

Title: Recommended Seismic Design Provisions for Hybrid Coupled Walls
Sponsor: American Society of Civil Engineers (ASCE)
Project Duration: 2005-2008

Synopsis: Hybrid Coupled Walls (HCW) are comprised of two or more reinforced concrete wall piers connected with steel coupling beams distributed over the height of the structure. Extensive research over the past several decades suggests that such systems are particularly well suited for use in regions of moderate to high seismic risk. This project reviewed the state-of-the-art in seismic modeling, analysis and design of hybrid coupled wall systems. Newly proposed design methodologies were then developed in both prescriptive and performance-based design formats.

Title: Development of an Enhanced Pushover Procedure for Performance-Based Seismic Evaluation Of Buildings
Sponsor: National Science Foundation (NSF)
Project Duration: 2002-2006

Synopsis: This project investigated inter-story drift and failure mechanisms that control the design of a structural system through a detailed study of various types of pushover techniques. The study was carried out on a selected group of six existing buildings for which instrumented data from recent earthquakes was available. The building models used in the analyses were calibrated to measured response thereby ensuring the reliability of the evaluation exercises. These evaluation tasks were conducted in two phases: the first focused on evaluating existing procedures, and the second phase an improved multi-mode and adaptive pushover technique.

Title: Use of Geopiers in Liquefiable Soils
Sponsor: GeoPier Foundation Company
Project Duration: 2006-2007

Title: Vulnerability of Bridge Piers to Collision by Heavy Vehicles
Sponsor: National Science Foundation (NSF)
Project Duration: 2003-2005

Synopsis: Accidental or malevolent vehicle/pier collisions can have serious implications both in terms of loss of human lives and damage to the transportation system and economy. This project employed detailed finite element simulation to study the effect of vehicle collision with various types of bridge piers. The vehicles were crashed into the piers at various speeds and the effect of the collision on the bridge piers evaluated. The results of this study were used to assess the then current AASHTO provisions for bridge design.

Title: Vehicle Collision with Bridge Piers
Sponsor: Florida DOT
Project Duration: 2001-2004

Synopsis: Accidental or malevolent vehicle/pier collisions can have serious implications both in terms of loss of human lives and damage to the transportation system and economy. This project employed detailed finite element simulation to study the effect of vehicle collision with various types of bridge piers. The vehicles were crashed into the piers at various speeds and the effect of the collision on the bridge piers evaluated. The results of this study were used to assess the then current AASHTO provisions for bridge design.

Title: Seismic Behavior and Design of Hybrid Wall Systems
Sponsor: National Science Foundation (NSF)
Project Duration: 1999-2004

Synopsis: This research focused on developing a better understanding of the seismic response of hybrid wall systems through detailed inelastic dynamic analyses. Two types of hybrid wall systems were considered, a) structural systems comprised of solid or perforated reinforced concrete shear walls and steel moment frames, and b) structural systems comprised of steel-girder-coupled shear walls and steel moment frames. The proposed project focused on the development of an existing finite element program to account for wall finite elements capable of simulating the complex behavior of wall panels. Prototype systems were designed using then existing provisions and subjected to suites of seismic excitation to study their response to strong shaking. The simulations focused on identifying the optimal degree of coupling between coupled shear walls and shed light on the interaction between shear walls and moment frames, established design oriented methods for determining the distribution of forces in the walls and frames, and assessed then current provisions for the design of hybrid wall systems and their components.

Title: Innovative Applications of Shape Memory Alloys in Wind and Seismic Hazard Mitigation
Sponsor: University of Central Florida
Project Duration: 2000-2001

Title: Monitoring of Steel Box Girders with Openings
Sponsor: Florida DOT
Project Duration: 2000-2002

Synopsis: Inspectors have to crawl through box girders on a regular basis to inspect them. Access hatches or holes on the underside of the boxes provide access to the inside of the girders. Hatches are usually provided before and/or after an expansion joint where bending moments are at their minimum. However, in many cases the spans covered by box girders are quite long. Furthermore, the bridges may be constructed as continuous girders over two or more supports. Hence distances between access hatches could become long and are likely to exceed the maximum recommended distance for safely rescuing trapped workers. The only viable solution to make the bridges safer for inspection crews is to place additional hatches thereby reducing the distance between access holes. This project made recommendations regarding appropriate locations where new access hatches could be added to existing steel box girder bridges without jeopardizing their structural integrity. The project also studied the effect of warping stresses on the response of existing bridges and the implications of such stresses on then existing design provisions.

Title: Inelastic Behavior and Design of Steel Frames With Semi-Rigid Connections
Sponsor: Nippon Steel Corporation
Project Duration: 1996-2002

Synopsis: The brittle fractures of welded moment connections in the Northridge and Kobe earthquakes heightened interest in the use of partially restrained connections as an alternative connection method for steel structures in seismic zones. In spite of concerns about the possibility of increased initial and post yield flexibility of semi-rigid frames, partially restrained connections were considered at the time of this project as an efficient and economical alternative to welded connections. This trend was reinforced by research conducted in the US, Europe and Japan that suggested that well-proportioned semi-rigid steel frames possess sufficient strength, stiffness, and ductility for seismic applications. Nonlinear dynamic analyses were employed to study the response of semi-rigid steel frames as alternatives to rigid moment frames. The work entailed development of a sophisticated nonlinear analysis model for semi-rigid steel connections.

Title: Presidential Major Equipment Award - Large Scale Structural Research Laboratory Equipment
Sponsor: University of Central Florida and BBM Engineers, Orlando, Florida
Other Participants: Sashi Kunnath and Ayman Okeil, Faculty members
Project Duration: 2000-2002

Synopsis: This project focused on obtaining equipment for the new Structures lab in the UCF Department of Civil and Environmental Engineering. The then new high bay lab had 40 ft high clearance, 3000 square feet of lab area, and a 6' deep 25' x 50' strong floor. The equipment purchased included: 1) two 100-kip servo-controlled actuators (MTS model 243.45T with 20" stroke), 60 gpm MTS hydraulic pump and an MTS control system; 2) 128-channel data acquisition system, 3) 200-kip Satec Universal Testing Machine, 4) 20-ton overhead crane; 5) steel reaction frame; and 6) several computers, hydraulic jacks, load cells, and other miscellaneous handling and testing equipment.

Title: Behavior and Design of Concrete Bridges Strengthened with F.R.P. Laminates
Sponsor: Florida DOT
Project Duration: 1999-2001

Synopsis: This project employed a computational approach combined with case studies to better understand the effect of FRP rehabilitation on inelastic bridge system behavior. The research addressed the following research questions:

  1. How is the safety level of a bridge system compromised if it is strengthened using FRP? How much strengthening is beneficial, and when is it detrimental? For example, since FRP rupture is brittle, would it be beneficial to design over-reinforced sections that fail by concrete crushing rather than under reinforced sections that fail by FRP rupture?
  2. How can a strengthening scheme be designed to account for important aspects of behavior, including flexure, shear, bond between FRP and concrete, stress concentration at FRP termination, fatigue, etc.
  3. How do the characteristics of the bridge structural system affect strength, ductility, and redundancy of the strengthened systems? In particular, how do bridge skew, length, number of girders, spacing of girders, number and strength of diaphragms impact system behavior.
  4. Can rehabilitation design guidelines be developed to account for the above issues?

Title: Validation of Evaluation Methods and Acceptance Criteria in FEMA 273: Case Studies of Instrumented Buildings
Sponsor: California Strong Motion Instrumentation Program
Project Duration: 1999-2001

Synopsis: This project critically assessed the nonlinear evaluation procedures and acceptance criteria in then evolving performance-based seismic codes. In particular, it focused on static pushover analysis, which at the time, was expected to become the design engineer's evaluation method of choice since it does not involve the complexities associated with nonlinear time history analysis. The project also assessed proposed performance-based design methodologies, focusing on the development of acceptance criteria based on performance levels. The project utilized available instrumented data from actual building response during earthquakes, which offered an unprecedented opportunity to understand the mechanics of building behavior and verify and validate both performance-based acceptance criteria and analytical methods needed to arrive at reasonable estimates of seismic demands. Detailed linear and nonlinear static and dynamic time-history analyses were conducted on a target set of four instrumented steel buildings to identify critical dynamic characteristics of the building response and arrive at realistic estimates of seismic demands based on performance objectives. The project offered a critical assessment of then current performance-based design criteria (comprising FEMA-273 and other evolving documents) and proposed modifications to existing guidelines.

Title: Strategies For Creating Access Holes in Existing Curved Steel Box Girders
Sponsor: Florida DOT
Project Duration: 1998-2000

Synopsis: Box girders are inspected periodically in search of flaws, damage, or any sign of deterioration. The interior of the box is accessed through what are called access hatches and is often a dangerous site due to the unusual temperatures and lack of ventilation. In general only two access holes are placed in each continuous segment; at the beginning and at the end. The access hatches are punched through the bottom flange of the girders at these locations. The segment ends are chosen because the bending moments are negligible and hence the strength of the bridge is not substantially affected by the presence of the holes. Furthermore, access holes in these locations are very accessible since they are close to the piers and therefore most designers take advantage of this obvious choice. Nevertheless, in many cases, the distance between segment end access hatches exceeds 600 feet, which is the limit that rescue crews can reach in the eventuality of an emergency.

This study looked into finding locations where additional access holes could be placed in order to decrease the distance between access hatches in existing bridges. This was achieved by conducting detailed elastic and inelastic finite element analyses of 19 box girder bridges representative of the State of Florida inventory. A detailed finite element model was created from four node shell elements and used in a case study of an existing bridge. Material and geometric nonliearities were included in the analyses which focused on the behavior and strength (both static and fatigue) of the bridge. A smaller but more detailed shell element model was also used to investigate flexural strength of a segment of the same bridge. In addition to the shell models, a beam-column finite element model that accounted for warping was created. This model is computationally more efficient than the shell models and was used in case studies of nineteen existing bridges. The force and moment envelopes due to dead and live load combinations following AASHTO's LRFD specifications were calculated. The construction sequence was considered in the analyses by adopting quasi-open section properties for dead loads and closed section properties for live loads.

Title: Large Scale Structural Research Laboratory Equipment
Sponsor: National Science Foundation (NSF)
Project Duration: 1998-2000

Synopsis: This project focused on obtaining equipment for the new Structures lab in the UCF Department of Civil and Environmental Engineering. The then new high bay lab had 40 ft high clearance, 3000 square feet of lab area, and a 6' deep 25' x 50' strong floor. The equipment purchased included: 1) two 100-kip servo-controlled actuators (MTS model 243.45T with 20" stroke), 60 gpm MTS hydraulic pump and an MTS control system; 2) 128-channel data acquisition system, 3) 200-kip Satec Universal Testing Machine, 4) 20-ton overhead crane; 5) steel reaction frame; and 6) several computers, hydraulic jacks, load cells, and other miscellaneous handling and testing equipment.

Title: Ductility of FR Welded Bolted Connections
Sponsor: SAC/FEMA Joint Venture
Other Participants: Sashi Kunnath, faculty member; Tameka Mikesell, MS student; Egill Vidarsson, MS student
Project Duration: 1996-1998

Synopsis: This project, which was a subtask of SAC/FEMA Task 5.3.1, was completed in April 1998 and has been published as SAC Report No. SAC/BD-98/01. The objectives of the study were 1) to develop a more thorough understanding of the inelastic behavior of pre-Northridge FR welded-bolted connections, and 2) lay the groundwork for the development of connection details that are not fracture critical. The project builds upon previous analytical and experimental studies and attempts to establish the effect of a number of key parameters on the ductility and potential for fracture of welded-bolted connections. The research addressed these objectives through detailed three-dimensional nonlinear finite element analyses of connection subassemblages.

Title: Curriculum Integration of Math, Science, Chemistry, and Engineering Classes
Other Participants: Richard Miller, faculty member
Project Duration: 1998.

Title: Strength, Redundancy, and Ductility of Reinforced Concrete Bridges Rehabilitated with FRP
Sponsor: Division of Sponsored Research, University of Central Florida
Project Duration: 1996-1998.