Department of Civil Engineering

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Contact Us

Main Campus
Nitschke Hall
Dr. Serhan Guner 
Phone: (419)530.8133
1610 N. Westwood Ave.
Nitschke Hall, Room: 3021
Toledo, Ohio 43607, USA
Fax (419)530.8006
serhan.guner@utoledo.edu

Research

Understanding and Predicting the Response of Cross-Laminated Timber subjected to a TFE Event

Millions of Americans are daily exposed to the risk of a tsunami-following-an-earthquake (TFE) event. Today, many US communities heavily rely on light-wood frame structures, which are highly vulnerable to tsunami forces. There is an urgent need to rethink the traditional civil infrastructure from a TFE perspective. The cross-laminated timber (CLT) combines the advantages of wood with a high strength that is comparable to other conventional alternatives such as reinforced concrete (RC).

 Wood  Wood

This project will study the performance of cross-laminated timber (CLT) buildings subjected to a tsunami following an earthquake (TFE) event (see the project framework above). A novel holistic analytical model will be created from the experimentally collected data. The created model will be used in a probabilistic study to create fragility curves and evaluate the expected tsunami performance of CLT buildings (see a sample fragility curve in the figure above). This study will contribute to the creation of a tsunami-resilient design procedure for CLT buildings while helping our profession and society progress towards designing tsunami-resilient communities. Project funding is currently being raised to conduct this study. If you are interested in contributing to this project, please contact Dr. Guner.

AN ANALYSIS METHODOLOGY FOR LESS-CONSERVATIVELY DETERMINING THE SHEAR CAPACITIES OF OVERLOADED PIER CAPS

‘Pier caps’ or ‘bent caps’ transfer the load from the girders to the columns. In Ohio, there are approx. 28,000 bridges with multiple pier caps for every bridge. When analyzed using the slender beam theory, a considerable number of pier caps are found shear-overloaded despite the fact that they don’t exhibit any noticeable cracking or signs of distress. This casts some doubt on the currently used analysis methods for pier caps. Rehabilitating all shear-overloaded pier caps will result in prohibitive costs. An accurate analysis method is needed to obtain more realistic shear capacities to correctly identify the overloaded pier caps.

 STM   STM

The main objective of this study is to create a practical and accurate analysis method, using the deep beam theory and the strut and tie method, for less-conservatively calculating the shear capacities of pier caps. This method will be used to create a macro-based analysis tool to generalize the findings and allow for applications in practice. The outcome of this study will have a potential to result in: (1) significant cost savings due to rehabilitating less number of bridges, (2) reduced construction work and associated traffic congestion, and (3) reduced hazard to construction crews and traveling public.

Understanding and Predicting the Hurricane Response of Adhesive Anchors 

Post-installed adhesive anchors are frequently used to attach non-structural components (NSC), such as mechanical equipment, telecommunication antenna towers, balcony railings, and solar panels, to concrete members. Damage reconnaissance studies demonstrate that NSC damage accounts for a significant portion of the total hurricane repair costs for buildings, and that anchorage failures are the most prevalent failure mode for NSCs.  In addition to the financial losses, the failure of NSC anchors can potentially result in: service interruptions, tearing of the roofing membrane and ensuing water intrusion, high-speed wind-borne debris, delays in post-storm recovery, and, in some cases, fatalities. Despite their frequent use, there is a critical gap in the current knowledge for the dynamic wind load behavior of post-installed adhesive anchors.

             AC AC 

This study aims to advance the current understanding of the dynamic wind-load behavior of adhesive anchors, create and validate a high-fidelity computation simulation method, and create a probabilistic analysis method to predict the risk of collapse. Project funding is currently being raised to conduct this study. If you are interested in contributing to this project, please contact Dr. Guner.

               FEM  Plot

Modeling the Response of Concrete Bridge Elements Containing Fiber Reinforced Polymer Bars

Every year, billions of dollars are spent in the US for repairing bridges; one of the major causes of deterioration is the corrosion of traditional reinforcing steel bars. As an alternative, FRP bars have excellent mechanical properties with a non-corrosive material matrix. As such, they present a significant potential to extend the service life and minimize the maintenance costs of concrete bridges. Despite the availability of various types of FRP bars and design code provisions, there is a lack of numerical modeling techniques to predict the load-deflection response and the failure mode of concrete members containing FRP bars.

               FRP  FRP

The objective of this study is to create a nonlinear finite element model to simulate the response of concrete members containing FRP bars up to their failure. Numerical modeling, reliability analyses, and experimental validation studies will be carried out to advance the exiting knowledge and numerical modeling capabilities.

  

A New Modeling Methodology for Concrete Elements Retrofitted with Externally Bonded FRPs

Fiber reinforced polymers (FRP) are widely used in the retrofit of concrete elements such as beams and columns. However, the system-level behavior of structures retrofitted with FRP is currently not well understood, and there is a lack of numerical simulation methods that can accurately account for the composite action and predict the structural response. Thus, an efficient staged analysis approach with an accurate FRP modeling methodology is required to provide a better understanding of the holistic structural behavior.

Bridge 

In this study, a finite element-based staged analysis methodology is proposed for deep beams retrofitted with externally bonded FRP fabrics (see the figure above). A two-stage verification study was conducted, including: constitutive modeling of critical material behaviors, and a full-scale structural modeling, both validated with experimental results available in the literature. The proposed analysis methodology was used to provide an effective retrofit solution for a real bridge bent and was able to capture the improved beam response, as shown in the figures below.

Crack   Curve

Resulting publication: Salgado, R. and Guner S. “A Modeling Methodology for Cap Beams Retrofitted with Externally Bonded Fiber Reinforced Polymers,” Engineering Structures (submitted in August 2017). 

A Comparative Study on Nonlinear Modeling Techniques for Performance-Based Earthquake Engineering

Performance-based earthquake engineering (PBEE) requires a large number of nonlinear dynamic analyses to statistically assess the performance of frame structures. The complexity and high computational demand of such procedures has hindered its use in practice. Simplified numerical modeling procedures can shorten the complexity and computational demand. However, there is a lack of understanding on the accuracy and reliability of the calculated responses from different numerical modeling techniques. This research aims to fill this knowledge gap by using the experimental data to verify the accuracy and computational demand characteristics of three different modeling approaches (shown in the figure below).

 TypesSeismic

Each created model has different levels of complexity and material behavior model comprehensiveness. To evaluate their simulation accuracy and computational demand, 126 numerical simulations were performed for a previously-tested RC frame using a PBEE framework. The accuracy of the calculated results was compared with the experimental values in terms of the base shear and first-story drift (shear-drift figure above), damage progression, and failure conditions. The computational demand of each model was also evaluated in terms of required model development, analysis, and result acquisition times. TimesThe influence of each modeling technique was compared using the calculated risk to a set of performance limits evaluated by means of fragility curves. The nonlinear models calculated significantly more accurate structural responses than the more-commonly used plastic-hinge model. The model development and result acquisition times were found to comprise a significant portion of the total computational demand of each model (see the figure). 

Resulting publication: Salgado, R. and Guner S. “A Comparative Study on Nonlinear Models for Performance-Based Earthquake Engineering,” Engineering Structures (submitted in Feb. 2017).

Creation of a Nonlinear Analysis Procedure for Frame Structures with Shear-Critical Behavior

Although modern design codes require concrete buildings to be designed for ductile and flexure-critical behaviour, many older, shear-critical structures exist in practice. Advanced nonlinear analysis methods with rigorous shear analysis capabilities are required to identify and accurately determine the load-displacement capacities of such frames. There is a critical gap in the knowledge for numerically simulating the shear behavior of building frames. 

  Frame 1Frame_2 Frame_3

In this study, an analytical procedure is formulated for the nonlinear analysis of reinforced concrete structures consisting of beams, columns, and shear walls under monotonic and pushover loads. The procedure is capable of accurately representing shear-related mechanisms coupled with flexural and axial behaviors. The formulations established include rigorous nonlinear sectional analyses of concrete member cross sections, using a distributed-nonlinearity fiber model, based on the Disturbed Stress Field Model (Vecchio, 2000). The proposed method is distinct from existing methods in that it allows for the inherent and accurate consideration of shear effects and significant second-order mechanisms within a simple modeling process suitable for analyzing large buildings. Assumptions regarding the anticipated behavior and failure mode of the system are not required.

                    Frame_5Frame_6

Resulting publications : Guner and Vecchio (2010a)Guner and Vecchio (2010b)Guner and Vecchio (2011) 

Understanding and Modeling the Behavior of Beam-Column Connections

For Seismic Loading: Beam-column connections undergo significant shear deformations and greatly contribute to story drifts during earthquake loading, yet their response is typically neglected in traditional frame analyses through the use of rigid end offsets. Although local joint models are available in the literature for the investigation of single, isolated joints, there is a lack of holistic frame analysis procedures simulating the joint behavior in addition to important global failure modes such as beam shear, column shear, column compression, and soft story failures.

                 Joint_1    Joint_2

The objective of this study is to capture the impact of local joint deformations on the global frame response in a holistic analysis by formulating a joint model into an existing global frame analysis framework. The joint element can simulate the joint shear deformations and bar-slip effects. Concrete confinement effects are also considered so that both older and modern joints can be modeled.  

                             Joint_3Joint_4

Resulting publications: Pan et al. (2017)

For Progressive Collapse Loading: When a reinforced concrete frame is subjected to progressive collapse due to the loss of a structural column, the surrounding elements typically experience a significant overload that may lead to their collapse. The rotational capacity of beams and, consequently, the beam-column connections is a critical factor determining the structural resiliency. Numerical models developed to assess the structural response under a progressive collapse situation must incorporate the beam-column joint response. In this study, a review of the beam-column joint modelling approaches, constitutive models, and the ease of their numerical implementation are presented. Some of these models are utilized to simulate the response of a previously-tested reinforced concrete frame. The calculated structural response parameters are compared to the experimental results, and the accuracy of each constitutive model is evaluated.                             

 Progressive_2Progressive_1Progressive_4

Resulting publications: Salgado and Guner (2017)   

Understanding and Modeling the Dynamic Behavior of Frame Elements

Subjected to Impact Loading: Heightened levels of terrorist threat have resulted in strategic structures, such as government and commercial buildings, requiring design for blast and impact resilience. Currently available methods employed in practice are typically based on overly simplistic macro models, however, reducing each structural component to a single-degree- of-freedom system. Moreover, the proper consideration of shear effects remains a major deficiency— even in the micro finite element methods—despite the fact that impact and blast loads tend to result in significant shear damage. The objective of this study is to formulate and verify a nonlinear frame analysis method capable of inherently and accurately representing shear effects for elements subjected to impact loads. A second focus is to account for the effects of the rate of loading within an explicit three-parameter time-step integration method. Furthermore, verification studies were undertaken using 11 previously tested specimens.

Impact_2

  Impact_1   Impact_3

Resulting Publications: Guner and Vecchio (2012)

Subjected to Earthquake Loading: Research studies conducted in the past number of decades have clearly demonstrated the importance of ductility in the survival of frames under strong ground motions. Modern seismic design codes, such as ACI 318, have thus incorporated stringent provisions requiring structures to be ductile and flexure-critical in their behaviors; however, many existing structures were constructed before the introduction of modern seismic design guidelines with nonductile and shear-critical details. There is an urgent need to perform safety assessments to identify and upgrade such structures. Currently available dynamic analysis methods, however, typically neglect shear-related effects. This omission may result in dangerously unconservative and unsafe response predictions. In this study, dynamic analysis formulations are established and incorporated in an existing global solution framework. The established method removes the current requirements of the assumed failure mode and sectional response hysteresis model, and thus is suitable for practical applications of seismic time-history analyses.

                                                 Seismic_1  Seismic_2

Resulting Publications: Guner and Vecchio (2012) Guner and Vecchio (2011)

Subjected to Blast Loading: Recent bomb attacks on high-profile buildings have created an increased awareness and demand for blast-resistant structures. The methods commonly employed for blast load analysis are either based on overly-simplistic “single-degree-of- freedom” (SDOF) approaches or overly-complex “finite element analysis” (FEA) software. SDOF approaches have limited applicability and fail to accurately model the behavior of reinforced concrete. FEA software is time-consuming, demands significant knowledge, and requires a large number of customized input parameters for reliable results. This study examines the accuracy, reliability, and practicality of a recently proposed analysis method by modeling 18 previously tested specimens using only the default material models and analysis options.

       Blast_1  Blast_2

Resulting Publications: Guner (2016)

Creation of Computer Programs and Spreadsheet

To enable the research and engineering communities to use the established formulations, a global simulation platform VecTor5 and a number of macro-enabled spreadsheets are created. These tools enable the dissemination of research findings and permit understanding the response of large, complete structures (as opposed the isolated structural components) subjected to various loading conditions. Program VecTor5 incorporates more than 16,000 lines of numerical calculation algorithms, and are being updated as new material behavior models and calculation methods are being created by the research team. Related Users’ Manuals and Bulletins are also composed by the research team to contribute to the correct use of these numerical simulation methods.

Resulting Publications: Computer Programs, user manuals, and user bulletins

Last Updated: 2/5/18