Ching Chiaw Choo

Strength of Rectangular Concrete Columns Reinforced with Fiber-Reinforced Polymer Bars

The strength interaction behavior of fiber-reinforced polymer (FRP) reinforced concrete (RC) columns is presented using an ultimate strength approach. A numerical integration technique is used to examine the slenderness effects of columns. The authors demonstrate that FRP RC columns have a propensity to undergo brittle-tension failure. This failure is generally sudden, and is associated with tension rupture of FRP bars when the strain in outer bar layer reaches or exceeds its ultimate load at the same time, or before, the concrete reaches its ultimate strain in compression. For RC columns reinforced with FRP bars, the current American Concrete Institute’s ratio limits may not be adequate.

Minimum Reinforcement Ratio for Fiber-Reinforced Polymer Reinforced Concrete Rectangular Columns

Two failure mechanisms were identified through a strength interaction analysis of rectangular concrete columns reinforced with fiber-reinforced polymer (FRP) bars. While the failure mechanisms identified were premature-compression failure and brittle-tension failure, the study demonstrated that, due to the low ultimate tensile strain for FRP bars, the brittle-tension failure was more likely to occur. Interaction design diagrams provide the process for identifying a reinforcement ratio that is greater than a minimum required ratio, which will identify the failures, and prevent brittle-tension failure. The authors recommend that only FRP reinforcing bars with ultimate compression strains larger than the concrete compression strain should be used in column applications.

Flexural Behavior of R/C Beams Strengthened with CFRP Sheets or Fabric

The resistance to electrochemical corrosion, high strength to weight ratio, larger creep strain, fatigue resistance, non-magnetic and non-metallic properties of carbon fiber reinforced polymer (CFRP) composites offer a viable alternative to bonding of steel plates in repair and rehabilitation of reinforced concrete structures. The objective of this investigation is to study the effectiveness of externally bonded CFRP sheets or fabric in increasing the flexural strength of concrete beams. Four-point bending flexural tests are conducted up to failure on nine concrete beams strengthened with different layouts of CFRP sheets and fabric, and on three beams with different layouts of anchored CFRP sheets. An analytical procedure, based on compatibility of deformations and equilibrium of forces, is presented to predict the flexural behavior of beams strengthened with CFRP sheets and fabric. Comparisons are made between the test results and the analytical calculations. Results of the testing showed that the flexural strength is increased up to 40% on beams strengthened with two layers of CFRP fabric, 49% on beams strengthened with two 1.42 mm thick CFRP sheets, and 58% on beams strengthened with two anchored 4.78 mm CFRP sheets.

SHEAR STRENGTH OF R/C BEAMS WRAPPED WITH CFRP FABRIC

The emergence of high strength epoxies has enhanced the feasibility of increasing the shear strength of concrete beams by wrapping with carbon fiber reinforced polymer (CFRP) fabric. The objective of this investigation is to evaluate the increase in shear strength of concrete beams wrapped with different configurations of CFRP fabric. Shear tests are conducted up to failure on two reinforced concrete control beams and twelve reinforced concrete beams wrapped with four different configurations of CFRP fabric. An analytical procedure is presented to predict the shear strength of beams wrapped with CFRP fabric. Comparisons are made between the test results and the analytical calculations. The shear strength is increased up to 33% on concrete beams wrapped with CFRP fabric at an angle of +/- 45 deg to the longitudinal axis of the beam.

Performance evaluation of bridges with structural bridge deck overlays (SBDO).

Structural Bridge Deck Overlay (SBDO) involves applying 6 to 10 in. (150 to 200 mm) of normal weight, class AA, reinforced concrete directly to a bridges original slab. The overlay is designed to increase the deck elevation to an extent that standard highway resurfacing procedures can continue uninterrupted up the edges of the bridge. Otherwise, excavation along the bridge approaches or jacking of the superstructure is required to insure proper elevation. Experimental static field tests were conducted on three different bridges: (1) Simply supported prestressed concrete I-girder bridge; (2) cast-in-place reinforced concrete continuous haunched girder bridge; and (3) cast-in-place reinforced concrete simple span bridge. Field tests were conducted prior to the concrete overlay process and following the application of the concrete overlay. Based on the results obtained in this research study, a significant advantage is noted due to the additional deck thickness. The addition of the SBDO increases the load carrying capacity of the bridge in addition to providing a wider bridge deck and new and code compliant barrier walls.

Seismic Evaluation of Bridges on and over the Parkways in Western Kentucky – Summary Report

This report (KTC-07-02/SPR246-02-1F) provides an overall summary on the seismic investigative study performed on bridges on/over the five parkways in Western Kentucky. The comprehensive study was further divided into the followings tasks, each reported separately as follows: (1) The first report of this study (KTC-07-03/SRP246-02-2F) involved data collection and field inspection of bridges on/over the parkways. The resulting inventory contains data of three hundred fifty-one (351) bridges on/over the parkways, detailing their construction type, soil profile, present condition, etc. (2) In KTC-07-04/SPR246-02-3F, a preliminary seismic evaluation and ranking was performed on all bridges within the inventory. Details of the evaluation and ranking procedure are outlined. In this task seventeen (17) bridges, that are deemed susceptible to major earthquakes, were identified. (3) Detailed seismic evaluations of the seventeen (17) bridges were subsequently carried out using time-history analysis for a projected 250-year seismic event. The results of the analysis are presented in KTC-07-05/SPR246-02-4F. (4) KTC-07-06/SPR246-02-5F presents the preliminary evaluation and ranking of bridge embankments along the parkways. (5) The last report, numbered KTC-07-07/SPR246-02-6F, provides the latest seismic hazard maps for the expected earthquake (EE), probable earthquake (PE), and maximum credible earthquake (MCE), which will be used in seismic analysis and design of highway infrastructures in Kentucky.

Retrofit of the Louisa-Fort Gay Bridge Using CFRP Laminates

This report details the processes pertaining to the repair and strengthening of the Louisa-Fort Gay bridge, Lawrence County, KY, using advanced composite materials. Site inspections revealed flexural cracks in the reinforced concrete girders of the continuous bridge structure. To determine the cause of these cracks, an evaluation was initiated based on vehicle classification and truck weight data. The results confirmed that certain reinforced concrete girders were stressed beyond the limits allowed by the AASHTO Code. A retrofit scheme using carbon fiber reinforced polymer (CFRP) composite was devised and the amount of CFRP laminates needed for flexural strengthening was determined from moment-curvature analysis. Retrofitting work began in September of 2003, and the project was completed in October of 2003. Crack gauges were installed at the affected areas to monitor the effectiveness of the retrofit. The bridge was inspected on a number of occasions and, as of September 28, 2006, no movement in the crack gauges has been observed.

Repair Using Steel Fiber Reinforced Polymer on US 150 Bridges

This report details the pre-construction monitoring, planning and design, and construction of the retrofit measures on the US150 bridge over Beech Fork River in Nelson County, Kentucky (KY) and Cartwright Creek bridge on the border of Washington-Nelson County, KY. All reinforced concrete girders of the five-span Beech Fork River bridge and three-span Cartwright Creek bridge of deck-girder construction had developed diagonal cracks near or at the transition of the variable-and-constant depth regions. To remedy the problem steel fiber reinforced polymer (SFRP) sheets were selected as the means of retrofit due to their strength and stiffness, as well as conformability and flexibility. Repair to the reinforced concrete girders was done by attaching the SFRP sheets to the vertical and bottom faces. Application of SFRP was quickly executed with the use of specialty epoxy designed for use with the steel wire sheets. Construction of the retrofit was completed in May of 2007.

Development and Deployment of Aluminum Bridge Decks

This report contains the analysis and retrofit of a steel truss bridge on KY 974 over Howard Creek in Clark County, Kentucky. The bridge had major corrosion and damage to the steel stringers, along with cracking and leaching occurring in the concrete bridge deck. The retrofit involves the replacement of the corroded steel stringers and the damaged concrete bridge deck. The original concrete deck was removed and replaced by light-weight high-strength aluminum deck panels. The aluminum deck panels, each 2-m wide, were assembled at the site and connected to each other and to the bottom steel stringers using special clamps and connectors. Following the new deck installation, the top surface was waterproofed and a new asphalt overlay was placed. The new bridge deck constructed of aluminum material significantly reduces the deck weight, while it also allows rapid construction due to prefabricated components. In addition, the new deck can now carry a HS20-44 truck weight, which the old concrete deck was not designed to carry.

Implementation of Remote Sensing Technology on the I-64 Bridge over US60

Remote sensing devices have been implemented on the I-64 Bridges over US60 in Franklin County, KY. One of the girders in the westbound bridge has been previously repaired due to unexpected fatigue cracking. The exterior girder in the eastbound bridge has shown signs of impacts due to the traversing trucks on US60. Sensing and recording devices such as strain and temperature gauges, infrared sensors, ultrasonic height detectors, and an accelerometer have been installed. Specifically, eleven strain gauges are used on the repaired girder, impacted girders, and girders adjacent to them. Two sets of infrared sensors, ultrasonic detectors, and video cameras are placed to capture the impacting truck(s). Overall structural responses will be studied through data collected from the strain and temperature gauges, and accelerometer. Data are stored on-site, but the investigator has the flexibility of transmitting or viewing the data, live or stored, via an internet connection.