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(1 - 8 of 8)
- Title
- Cyclic and Impact Resistance of FRP Repaired Poles.
- Creator
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Mohsin, Zainab, Mackie, Kevin, Makris, Nicos, Nam, Boo Hyun, University of Central Florida
- Abstract / Description
-
Sign and signal structures involved in vehicular accidents are often partially damaged, and it ispossible to repair them instead of replacing them, even when the extent and severity of the damageare substantial. The replacement of these poles is costly and involves interruption for pedestriansand traffic. Therefore, some trials were performed to retrofit these poles in-situ with low cost andshort time. Previous research has substantiated that the damage can decrease the strength of thethese...
Show moreSign and signal structures involved in vehicular accidents are often partially damaged, and it ispossible to repair them instead of replacing them, even when the extent and severity of the damageare substantial. The replacement of these poles is costly and involves interruption for pedestriansand traffic. Therefore, some trials were performed to retrofit these poles in-situ with low cost andshort time. Previous research has substantiated that the damage can decrease the strength of thethese structures with increasing the dent depth and the use of externally-bonded fiber-reinforcedpolymer (FRP) composites are beneficial to repair them. The composite systems were comprisedof glass or basalt fibers paired with epoxy or polyurethane matrices. The effectiveness of FRPin repairing the damaged poles was demonstrated in previous tests on dented poles using 3-point,4-point, and cantilever bending tests. The repair systems were able to develop the load carryingcapacity of the damaged poles, and their behaviors were controlled by various types of failuremodes like yielding of the metallic substrate, FRP tensile rupture, FRP compressive buckling, anddebonding of FRP from the substrate.This thesis investigates the resistance of repaired full-scale metallic poles retrieved from the fieldfor monotonic, cyclic, and impact loading. These poles, which have rounded and multi-sided crosssections with and without access ports, were dented in the field or dented mechanically in thelaboratory and repaired with the same repair systems mentioned previously. Six of these poleswere mounted horizontally in a cantilever configuration to test them monotonically, while three ofthem were tested cyclically. In both tests, the load was applied as a point load at 9 ft from the baseplate. Additionally, two poles were mounted vertically using a cantilever configuration to test themfor impact. This test was performed by hitting the poles using an impact pendulum with a 1100 kgmass.The results of static tests show that the repair systems failed because of the aforementioned failuremodes. However, most of the failure was located outside the dented region, which indicates theeffectiveness of these repair systems in restoring the capacity of the damaged area. During thefatigue tests, the repair experienced no damage before weld rupture in the original steel tube-baseplate connection. Moreover, the repair systems proved their effectiveness in resisting the impactload, because they were ruptured at the contact region between the pole and the impactor at thetime the poles were deformed at the free side of the poles, as well as the impact side, during thetest.In all these tests, the access ports affected the behavior of the repaired poles. Depending on thegeometry of the pole, metal substrate, and dent depth and location, FRP repair system recommendationswill be presented.
Show less - Date Issued
- 2015
- Identifier
- CFE0005846, ucf:50936
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005846
- Title
- Effect of Load Path and Failure Modes on Seismic Response of Regular Bridges.
- Creator
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Darwash, Haider, Mackie, Kevin, Chopra, Manoj, Makris, Nicos, Bai, Yuanli, University of Central Florida
- Abstract / Description
-
Bridges are essential infrastructure constituents that have been studied for centuries. Typically,seismic bridge design and assessment utilize simplified modeling and analysis techniques basedon one-dimensional spine elements and zero-length springs/hinges. The geometry of the elementsand calibration of parameters are based on assumptions for the lateral load path and failure modes,e.g., sacrificial backwall and shear keys, neglecting wing walls, and strength based on backfillalone. These...
Show moreBridges are essential infrastructure constituents that have been studied for centuries. Typically,seismic bridge design and assessment utilize simplified modeling and analysis techniques basedon one-dimensional spine elements and zero-length springs/hinges. The geometry of the elementsand calibration of parameters are based on assumptions for the lateral load path and failure modes,e.g., sacrificial backwall and shear keys, neglecting wing walls, and strength based on backfillalone. These assumptions have led to observations of underestimated resistance, overestimateddisplacement demands, and unpredicted damage and failure mode. The focus of the study is onordinary standard bridges with continuous reinforced concrete box girder superstructures and seattypeabutments.A bridge component calibration study was conducted first using simplified (spine models with 1Delements and springs) and three-dimensional nonlinear continuum finite element models (FEM).Model responses were compared with experimental results to identify the drawbacks in the simplifiedmodels and verify the adequacy of the material nonlinearities and analysis procedures. Thecomponents include a T-girder, abutment backfill, abutment shear key, elastomeric bearing pad,and a bridge pier. Results show the simplified models do not capture damage propagation andfailure mode in the shear key case, nonlinear behaviors in beams with high aspect ratios (or deepbeam action), and underestimate the strength and overestimate the stiffness for the backfill case.The component models (both simplified and continuum) were then used in studying the nonlinearstatic behaviors of key bridge lateral-load resisting substructures, namely abutments and bents.For the abutment subsystem, cases with and without backfill and several back wall constructionjoint configurations for the longitudinal direction, with monolithic shear key and shear key withconstruction joint for the transverse direction, and boundary conditions in the transverse direction were considered. Abutment subsystem results showed simplified models underestimate the resistanceby 10-60%, neglect back wall and wing wall structural contributions, and localize damagein the back fill relative to the continuum models. For the bent subsystem, a full bridge systemthat considers material nonlinearity and damage in the bent segment only was adopted to determinethe effect of the finite bent cap or superstructure-to-column connection. Inelastic behaviorand damage was included in the columns, bent cap, and a superstructure segment with a lengththat correspond to the dead load moment inflection point. The other superstructure segments andthe pile cap were modeled as elastic. Bent subsystem results showed simplified models overestimatethe stiffness, induce excessive flexibility and deformation in the cap beam, and overestimatecolumns' deformations.Due to the differences observed in the abutment subsystem, and the potential impact of the abutmentbehavior on the seismic response of the whole bridge system, dynamic studies on the bridgesystem were conducted using four abutment parameters: abutment stiffness and strength in eachof the longitudinal and transverse directions. Two models were developed to conduct nonlineartime history analysis: an equivalent single-degree-of-freedom (SDOF) model for each of the longitudinaland transverse directions, and a 3D spine bridge model. Constant ductility analyses wereconducted using the SDOF systems, while standard probabilistic seismic demand analysis wasused on the spine systems.Results revealed that, besides the columns yielding, the abutment has an early and significant contributionto the behavior. The SDOF system results showed that increasing the abutment stiffnessor strength reduces the system displacement demand and increases the system forces. The consequenceof such increase in the forces is mobilizing significant amount of force in the abutments,causing inelastic response. The full bridge study also confirmed the SDOF results and showedthat the abutment forces are more than 200% of the columns forces that would result in the sameaftereffect observed in the SDOF system.
Show less - Date Issued
- 2017
- Identifier
- CFE0006869, ucf:51759
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006869
- Title
- hydro-thermo-mechanical behavior of concrete at elevated temperatures.
- Creator
-
Al Fadul, Manar, Mackie, Kevin, Makris, Nicos, Chopra, Manoj, Kar, Aravinda, University of Central Florida
- Abstract / Description
-
In the light of recent tragic events, such as, natural disasters, arson and terrorism, studying the thermo mechanical behavior of concrete at elevated temperatures has become of special concern. In addition, the fact that concrete has been widely used as a structural material in many critical applications, such as high rise buildings, pressure vessels, and nuclear plants, enhances the potential risk of exposing concrete to high temperatures. Accordingly, the potential damage to large-scale...
Show moreIn the light of recent tragic events, such as, natural disasters, arson and terrorism, studying the thermo mechanical behavior of concrete at elevated temperatures has become of special concern. In addition, the fact that concrete has been widely used as a structural material in many critical applications, such as high rise buildings, pressure vessels, and nuclear plants, enhances the potential risk of exposing concrete to high temperatures. Accordingly, the potential damage to large-scale structures during the course of the fire, besides the possible loss of human life, emphasizes the necessity to better understand the thermo-structural behavior and failure mechanism of concrete exposed to elevated temperatures. In this study, a one-dimensional model that describes coupled heat and mass transfer phenomena in heated concrete was developed. The mathematical model is based on the fully implicit finite difference scheme. The control volume approach was employed in the formulation of the finite difference equations. The primary variables considered in the analysis are temperature, vapor density, and pore pressure of the gaseous mixture. Several phenomena have been taken into account, such as evaporation, condensation, and dehydration process. Temperature, pressure, and moisture dependent properties of both gaseous and solid phases were also considered. Moreover, the proposed model is capable of predicting pore pressure values with a sufficient accuracy, which could be significantly important for the prediction of spalling and fire resistance of concrete. The two dimensional coupled heat and mass transfer problem was then studied by extending the proposed one dimensional model so that it can be applicable in solving two-dimensional problems. Output from the numerical model showed that the maximum values of temperature, pressure, and moisture content occur in the corner zone of the concrete cross section, in which the pore pressure builds up right next to the moisture pocket towards the center. In addition, the model demonstrates the capability to solve the coupled problem in situations involving non symmetric boundary conditions, in which conducting a one dimensional analysis is of no use. The contour plots of the temperature, pressure, and moisture were also presented.Simulation results clearly indicate the capability of the proposed model to capture the complex behavior of the concrete exposed to elevated temperatures in two dimensional systems and to adequately predict the coupled heat and mass transfer phenomena of the heated concrete over the entire flow domain. In order to predict the structural behavior of reinforced concrete members exposed to elevated temperatures, a three-dimensional fiber beam model was developed in this study to compute the mechanical responses of reinforced concrete structures at elevated temperatures by using the well-known sectional analysis approach. The temperature distributions obtained from the two-dimensional coupled heat and mass transfer analysis were used as an input to the strength analysis. The model also accounts for the various strain components that might generate in concrete and steel due to the effect of high temperatures. The constitutive models that describe the structural behavior of concrete and steel at elevated temperatures were also presented. In order to establish the validity of the proposed fiber model, a sequentially coupled thermo mechanical analysis was implemented, in which the model predictions were compared against measured data from tests with good qualitative agreement. The developed model can be considered as an efficient and powerful tool to promptly assess the structural behavior and the integrity of the structure during emergency situations, such as fire events.
Show less - Date Issued
- 2017
- Identifier
- CFE0006551, ucf:51340
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006551
- Title
- Role of Force Resultants Interaction on Fiber Reinforced Concrete.
- Creator
-
Chan, Titchenda, Mackie, Kevin, Catbas, Necati, Makris, Nicos, University of Central Florida
- Abstract / Description
-
Ultra-high performance concrete (UHPC) is a recently developed concrete gaining a lot of interest worldwide, and a lot research has been conducted to determine its material properties. UHPC is known for its very high strength and high durability. Association Francaise de Genie Civil (AFGC) has defined UHPC as a concrete exhibiting compressive strength greater than 150 MPa (22 ksi). To utilize the full compressive strength of UHPC, complementary tension reinforcement is required. A recent...
Show moreUltra-high performance concrete (UHPC) is a recently developed concrete gaining a lot of interest worldwide, and a lot research has been conducted to determine its material properties. UHPC is known for its very high strength and high durability. Association Francaise de Genie Civil (AFGC) has defined UHPC as a concrete exhibiting compressive strength greater than 150 MPa (22 ksi). To utilize the full compressive strength of UHPC, complementary tension reinforcement is required. A recent research study to find light weight yet high strength alternative deck systems for Florida movable bridges demonstrated that a composite UHPC and high strength steel (HSS) reinforcement deck system is a viable alternative. However, failure modes of the deck system observed during experimental testing were shear failures rather than flexural failures. Interestingly, the shear failures were ductile involving large deformations and large sectional rotations.The purpose of this research is to quantify the sensitivity of UHPC structural member mechanical response to different shear and normal stress demands, and investigate the underlying failure modes. An experimental investigation on small-scale prisms without reinforcement, prisms reinforced with ASTM Grade 60 steel, and prisms reinforced with high strength steel was carried out to capture load-deflection behavior as well as modes of failure of the UHPC specimens. Numerical analysis based on modified compression field theory (MCFT) was developed to verify experimental results at the section level, and further verification using continuum methods was performed using MCFT/DSFM (disturbed stress field method) based finite element analysis software (VecTor2).Results from the numerical analysis could reasonably predict the load-displacement as well as the failure modes of the experimental specimens. Obvious flexural failure was observed on unreinforced UHPC specimens where wide crack opening gradually widened at the bottom fiber of the concrete to the loading position. Whereas UHPC-Grade 60 steel specimens experienced ductile flexural failure with similar wide crack opening after the rebar yielded. On the other hand, UHPC-MMFX specimens largely failed in shear from a diagonal tension crack and crush of concrete top fiber.
Show less - Date Issued
- 2014
- Identifier
- CFE0005471, ucf:50394
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005471
- Title
- Seismic Response of Moment Resisting Frames Coupled with Rocking Walls.
- Creator
-
Aghagholizadeh, Mehrdad, Makris, Nicos, Catbas, Necati, Mackie, Kevin, Kauffman, Jeffrey L., University of Central Florida
- Abstract / Description
-
This study investigates the inelastic response of yielding structures coupled with rocking walls. This topic is of major significance in the design of tall moment-resisting buildings, since during recent major earthquakes several tall, moment-resisting frames that had been designed in an accordance to the existing seismic code provisions, exhibited a weak-story failure. Utilization of this structural system can help reducing maximum story drifts, prevents weak story failure and minimize...
Show moreThis study investigates the inelastic response of yielding structures coupled with rocking walls. This topic is of major significance in the design of tall moment-resisting buildings, since during recent major earthquakes several tall, moment-resisting frames that had been designed in an accordance to the existing seismic code provisions, exhibited a weak-story failure. Utilization of this structural system can help reducing maximum story drifts, prevents weak story failure and minimize residual deformation of the structure. This study first examines different configurations of both stepping rocking walls and pinned rocking walls that have been reported in the literature.Next, effect of additional vertical tendons or vertical damping devices in maximum response of the system is investigated. This research first derives the nonlinear equations of motion of a yieldingoscillator coupled with a rocking wall and the dependability of the one-degree of freedom idealization is validated against the nonlinear time-history response analysis of a 9-story moment-resisting frame coupled with a rocking wall. This research finally concludes that, stepping wall suppresses peak and permanent displacements, with the heavier wall being most effective. In contrast, the pinned rocking wall increases in general the peak inelastic displacements and the permanent displacements. While, the coupling of weak building frames with rocking walls is an efficient strategy that controls inelastic deformations by enforcing a uniform interstory-drift distribution, therefore, avoiding mid-story failures, the study shows that even for medium-rise buildings the effect of vertical tendons on the inelastic structural response is marginal, except for increasing the vertical reactions at the pivoting points of the rocking wall. Additionally, The SDOF idealization presented in this study compares satisfactory with finite-element analysis of a 9-story steel SAC building coupled with a stepping rocking wall; therefore, the SDOF idealization can be used with confidence for preliminary analysis and design.
Show less - Date Issued
- 2018
- Identifier
- CFE0007301, ucf:52157
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007301
- Title
- Mechanistic Behavior of UHPC and UHPC Composite Structural Components.
- Creator
-
Al-Ramahee, Munaf, Mackie, Kevin, Makris, Nicos, Nam, Boo Hyun, Gou, Jihua, University of Central Florida
- Abstract / Description
-
The resistance of reinforced concrete is mobilized through the composite action of two materials with different mechanical behaviors and physical features. Enabling the composite action requires a transfer mechanism between the concrete and the reinforcement which is referred to as bond. The bond model can be defined as a traction-slip relation tangent to the interface. The bond strength between different types of concrete, internal reinforcement, and external reinforcement has been of...
Show moreThe resistance of reinforced concrete is mobilized through the composite action of two materials with different mechanical behaviors and physical features. Enabling the composite action requires a transfer mechanism between the concrete and the reinforcement which is referred to as bond. The bond model can be defined as a traction-slip relation tangent to the interface. The bond strength between different types of concrete, internal reinforcement, and external reinforcement has been of interest to structural engineers for decades. Experimental tests have been carried out to validate the existing bond models and introduce new bond models for special cases of concrete or reinforcement. The effect of various parameters on the bond stress, such as bar diameter, concrete compressive strength, presence of fibers, cyclic loading, etc. have been investigated. However, little attention has been directed to the contribution of normal (to the interface) stress and state of stress of the substrate layer on the mechanical response of the interface. Since the state of stress (tangential, normal, and substrate) within each type of experimental test is different, the resulting bond models are not consistent.Behavior of ultra-high performance concrete (UHPC) composite flexural members are studied using experimental, analytical, and numerical approaches in this research. A new bond-slip model is proposed that contains an explicit representation of the normal stress and constitutive model of the substrate. The parameters of the model were calibrated from beam and pullout tests using UHPC and HSS. The calibrated results showed consistency in the material point behavior between the pullout and beam test although the states of stress were different. The effect of the normal force was verified throughout a numerical model compared with experimental flexural tests. Single and double lap shear tests were carried out for UHPC and FRP, and parameters of the bilinear model were calibrated and used in the finite element model of the new composite deck.A new lightweight composite deck system is proposed that uses fiber reinforced polymers (FRP) bonded to UHPC using vacuum-assisted resin transfer molding. The high-performance deck system has application in deck design and replacement for bridges with weight restrictions as well as for accelerated bridge construction. Results show the deck satisfies strength and serviceability criteria under monotonic load. The bond strength between the UHPC and the glass fiber reinforced polymers (GFRP) plays a significant role in the performance of the proposed deck and controls the behavior of the system. However, live loads on bridges are inherently cyclic and therefore research on serviceability and fatigue behavior of UHPC and UHPC composite members were carried out. The UHPC beams were strengthened using glass GFRP plates on compression side to obtain data that could be utilized for the future design. The effect of fatigue loading on the interfacial shear stress between UHPC and GFRP was also investigated and it is found to be minor under low load level. However, a noticeable progression in the interfacial shear stress was found for the higher load ratio.
Show less - Date Issued
- 2016
- Identifier
- CFE0006431, ucf:51464
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006431
- Title
- Load Estimation, Structural Identification and Human Comfort Assessment of Flexible Structures.
- Creator
-
Celik, Ozan, Catbas, Necati, Yun, Hae-Bum, Makris, Nicos, Kauffman, Jeffrey L., University of Central Florida
- Abstract / Description
-
Stadiums, pedestrian bridges, dance floors, and concert halls are distinct from other civil engineering structures due to several challenges in their design and dynamic behavior. These challenges originate from the flexible inherent nature of these structures coupled with human interactions in the form of loading. The investigations in past literature on this topic clearly state that the design of flexible structures can be improved with better load modeling strategies acquired with reliable...
Show moreStadiums, pedestrian bridges, dance floors, and concert halls are distinct from other civil engineering structures due to several challenges in their design and dynamic behavior. These challenges originate from the flexible inherent nature of these structures coupled with human interactions in the form of loading. The investigations in past literature on this topic clearly state that the design of flexible structures can be improved with better load modeling strategies acquired with reliable load quantification, a deeper understanding of structural response, generation of simple and efficient human-structure interaction models and new measurement and assessment criteria for acceptable vibration levels. In contribution to these possible improvements, this dissertation taps into three specific areas: the load quantification of lively individuals or crowds, the structural identification under non-stationary and narrowband disturbances and the measurement of excessive vibration levels for human comfort. For load quantification, a computer vision based approach capable of tracking both individual and crowd motion is used. For structural identification, a noise-assisted Multivariate Empirical Mode Decomposition (MEMD) algorithm is incorporated into the operational modal analysis. The measurement of excessive vibration levels and the assessment of human comfort are accomplished through computer vision based human and object tracking, which provides a more convenient means for measurement and computation. All the proposed methods are tested in the laboratory environment utilizing a grandstand simulator and in the field on a pedestrian bridge and on a football stadium. Findings and interpretations from the experimental results are presented. The dissertation is concluded by highlighting the critical findings and the possible future work that may be conducted.
Show less - Date Issued
- 2017
- Identifier
- CFE0006863, ucf:51752
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006863
- Title
- POLYURETHANE FIBER REINFORCED POLYMER STRENGTHENING OF SHEAR DEFICIENT REINFORCED CONCRETE BEAMS.
- Creator
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Al-Lebban, Yasir, Mackie, Kevin, Chopra, Manoj, Makris, Nicos, Gou, Jihua, University of Central Florida
- Abstract / Description
-
The use of externally-bonded fiber-reinforced polymer (FRP) composites has been established as an effective means for the strengthening of shear-deficient reinforced concrete (RC) flexural members. Epoxy-based wet layup systems were predominantly employed in previous studies. In this study, carbon FRP pre-impregnated with polyurethane resin is utilized in strengthening shear-deficient RC beams and compared to an epoxy resin. Fourteen small-scale (96 in span, 6 in width, and 12 in height) and...
Show moreThe use of externally-bonded fiber-reinforced polymer (FRP) composites has been established as an effective means for the strengthening of shear-deficient reinforced concrete (RC) flexural members. Epoxy-based wet layup systems were predominantly employed in previous studies. In this study, carbon FRP pre-impregnated with polyurethane resin is utilized in strengthening shear-deficient RC beams and compared to an epoxy resin. Fourteen small-scale (96 in span, 6 in width, and 12 in height) and five large-scale (132 in span, 12 in width, and 17 in height) flexural specimens were tested, considering FRP system type (polyurethane versus epoxy), size effect, shear span-to-depth ratio, FRP configuration (U-wraps versus side bonding), and FRP scheme (sheets versus strips with 45o or 90o). Experimental strength testing under four-point loading demonstrated similar or enhanced shear capacity when strengthening by the polyurethane compared to the epoxy composite systems.The shear behavior of polyurethane-based FRP composite system is investigated in this research using analytical and numerical approaches. A closed-form mechanics-based analytical model, utilizing the principle of effective FRP stress and upper-bound theorem, illustrated that the shear behavior and debonding mechanism were dependent on both FRP composite and bond characteristics. The analytical model is expressed in terms of shear crack opening crossed by the FRP laminate and gives good agreement with experimental results. The finite element analysis (FEA) model shows that the stresses in the FRP are not in single direction as in the coupon tests, and the biaxial stress states should be taken into consideration.The structural behavior of RC members strengthened with externally-bonded FRP composites is mobilized through the composite action technique. Bond stress can be defined as the shear stress acting in the interface between FRP and concrete. It is of crucial importance to evaluate the failure mode behavior. Debonding (loss of adhesion) failure is one of the most common modes of failure encountered in shear strengthening RC members in practice. Numerous constitutive bond-slip models have been proposed and derived numerically and mathematically based on experimental data with an assumption that the FRP width bp is taken as a variable and all stresses or strains at the same longitudinal coordinate (L direction) are uniform. No attention has been given to study the bond states of stress which are mainly altered by the inclined shear cracks in concrete. A new bond-slip law was proposed to address the biaxial two-dimensional (2D) states of stress problem. Numerical solution by finite difference (FD) was conducted to solve four partial differential equations per node (2 for FRP and 2 for concrete in each direction) with appropriate boundary conditions to obtain the stresses, slips, and strains based on the proposed bond-slip model. A new experimental setup was proposed to represent the 2D bond-slip model by lap shear tests in both directions by laminating two perpendicular strips on concrete blocks with the proposed strain profile. Experimental calibration has been carried out by using nonlinear least-squares regression (fitting) of the experimental strain data with the numerical FD equations to obtain the bond-slip parameters for the 2D FRP-to-concrete polyurethane interface system.
Show less - Date Issued
- 2017
- Identifier
- CFE0006852, ucf:51737
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006852
