Kuo-Chun Chang

Large-Scale Experimental Study of Precast Segmental Unbonded Posttensioned Concrete Bridge Columns for Seismic Regions

The seismic behavior of the proposed precast segmental unbonded posttensioned concrete bridge columns for use in regions of high seismicity was investigated experimentally. Posttensioning tendons were placed in the hollow core of the columns and left unbonded with the surrounding concrete to decrease prestress loss during earthquakes. Bonded mild steel bars continuous across the segment joints, also referred to as energy dissipation (ED) bars, were used to enhance the seismic resistance of the columns. The bars were unbonded at the critical joint to avoid premature low cycle fatigue failure. The objectives of this study were to (1) verify the proposed construction method and seismic detailing for the ED bars and (2) investigate the seismic behavior of the columns with different ED bar ratios and posttensioning forces. Four large-scale specimens were designed and tested with lateral cyclic loading. Test results showed that the proposed construction method and seismic detailing for the ED bars were effectiv...

Real-time monitoring of local scour by using fiber Bragg grating sensors

Local scour is one of the major factors for bridge failure. Scour failures tend to occur suddenly and without prior warning or sign of distress to the structure. Two types of real-time monitoring systems for bridge scour, using fiber Bragg grating (FBG) sensors, have been developed and tested in the laboratory. These FBG scour-monitoring systems can measure both the processes of scouring/deposition and the variations of water level. Several experimental runs have been conducted in the flume to demonstrate the applicability of the FBG systems. The experimental results indicate that the real-time monitoring system has the potential for further applications in the field.

Flood scour monitoring system using fiber Bragg grating sensors

The exposure and subsequent undermining of pier/abutment foundations through the scouring action of a flood can result in the structural failure of a bridge. Bridge scour is one of the leading causes of bridge failure. Bridges subject to periods of flood/high flow require monitoring during those times in order to protect the traveling public. In this study, an innovative scour monitoring system using button-like fiber Bragg grating (FBG) sensors was developed and applied successfully in the field during the Aere typhoon period in 2004. The in situ FBG scour monitoring system has been demonstrated to be robust and reliable for real-time scour-depth measurements, and to be valid for indicating depositional depth at the Dadu Bridge. The field results show that this system can function well and survive a typhoon flood.

Compressive Behavior of Steel-Fiber-Reinforced Concrete with a High Reinforcing Index

Compression tests on cylinders were performed to characterize the compressive stress-strain behavior of steel fiber-reinforced concrete (SFRC) with a high reinforcing index. The reinforcing index, defined as the product of the volume fraction and the aspect ratio of the fibers, of steel fibers examined was as high as 1.7. Hooked-end fibers of various lengths and aspect ratios were considered. The test results indicated that a higher reinforcing index was associated with a higher strain at the peak stress and a higher toughness of SFRC, up to a reinforcing index approximately equal to that corresponding to a 2% fiber volume fraction. Adding steel fibers had little effect on the modulus of elasticity and compressive strength of SFRC. Long steel fibers and fibers with a lower aspect ratio resulted in a larger increase of the toughness of SFRC. On the basis of the test results, analytical models of the stress-strain curve in compression and toughness of SFRC with a reinforcing index up to 1.7 are developed.

Online monitoring of highway bridge construction using fiber Bragg grating sensors

The civil engineering community is becoming increasingly interested in monitoring structural behavior and in assessing its corresponding integration. In this paper, fiber Bragg grating (FBG) sensors were installed to investigate the in situ characteristics of the hydration progress period and the curing process of highway bridge construction. Moreover, the security and serviceability of a bridge can be changed by material proprieties such as shrinkage and creep, which is correlated with the prestressing strain and settlement during the support frame removal. The response and effectiveness of the schedule at every step during the prestressing process, and during the support frame removal, were also examined. It appeared that an FBG sensor was clearly shown to be a smart sensor candidate for function integration and response of a highway bridge during both its construction and service life.

Ground Motion Duration Effects on Hysteretic Behavior of Reinforced Concrete Bridge Columns

AbstractThis study examined seismic behavior under long-duration ground motion in flexural-dominated reinforced concrete bridge columns designed per modern seismic design codes. Two column specimens with identical design parameters were tested. The first column (named CLC) was tested using a long-duration loading protocol developed to represent the number of response cycles expected under long-duration ground motions. The second column (named COC) was tested using a baseline loading protocol with one cycle for each drift loading to obtain baseline behavior for comparison with the behavior of the CLC column. Test results showed that the CLC column had a similar peak strength but a lower ductility capacity compared with the COC column. When drift was 3% or less, the columns showed a similar hysteretic envelop response. However, degradation of stiffness was greater in the CLC column. When drift exceeded 3%, the CLC column started to show greater strength degradation. The relationship between the damage index...

Online health monitoring and safety evaluation of the relocation of a research reactor using fiber Bragg grating sensors

This paper demonstrates the reliability and accessibility functions of fiber Bragg grating (FBG) sensors in a radiation structural health monitoring and safety evaluation application. FBG sensors, dial gages and conventional resistance strain gages (RSGs) were attached to the temporary H-beam frame, and distributed below the path of the rail tracks for online safety measurements during the process of moving the structure of the research reactor. The results showed the high level of performance of the FBG sensors for an online structural health monitoring system. The measurement data from the FBG monitoring system were comparable to the theoretical calculation results and the FEM simulations as the movement progressed. The result of this investigation also clearly demonstrates that FBG sensors can overcome the harsh environments of electric and magnetic interference, while conventional RSG sensors are subject to serious fluctuations providing useless feedback.

Seismic performance of an existing bridge with scoured caisson foundation

This paper presents in-situ seismic performance tests of a bridge before its demolition due to accumulated scouring problem. The tests were conducted on three single columns and one caisson-type foundation. The three single columns were 1.8 m in diameter, reinforced by 30-D32 longitudinal reinforcements and laterally hooped by D16 reinforcements with spacing of 20 cm. The column height is 9.54 m, 10.59 m and 10.37 m for Column P2, P3, and P4, respectively. Column P2 had no exposed foundation and was subjected to pseudo-dynamic tests with peak ground acceleration of 0.32 g first, followed by one cyclic loading test. Column P3 was the benchmark specimen with exposed length of 1.2 m on its foundation. The exposed length for Column P4 was excavated to 4 m, approximately 1/3 of the foundation length, to study the effect of the scouring problem to the column performance. Both Column P3 and Column P4 were subjected to cyclic loading tests. Based on the test results, due to the large dimension of the caisson foundation and the well graded gravel soil type that provided large lateral resistance, the seismic performance among the three columns had only minor differences. Lateral push tests were also conducted on the caisson foundation at Column P5. The caisson was 12 m long and had circular cross-sections whose diameters were 5 m in the upper portion and 4 m in the lower portion. An analytical model to simulate the test results was developed in the OpenSees platform. The analytical model comprised nonlinear flexural elements as well as nonlinear soil springs. The analytical results closely followed the experimental test results. A parametric study to predict the behavior of the bridge column with different ground motions and different levels of scouring on the foundation are also discussed.

Life-cycle evaluation of deteriorated structural performance of neutralised reinforced concrete bridges

For existing reinforced concrete (RC) bridges, the structural performance is highly dependent on the changing properties of concrete and reinforcing steel due to neutralisation-induced corrosion. As neutralisation progresses, the corrosion could become serious enough to deteriorate not only the serviceability, but also the maintainability, of the structural performance. To study the influence of neutralisation on the existing RC bridges, the inspected data and test results collected from 21 bridges in Taiwan were examined to obtain the essential parameters through regression analyses. The regressive parameters related to service time can be employed in evaluating the variation of material and sectional properties in both reinforcements and concrete, and, accordingly, the change of structural performance from time to time could be obtained quantitatively via structural analysis. As a consequence, the performance degradation curve of an existing RC bridge can be predicted and, if necessary, the appropriate timing for repair or retrofit could be suggested. The results obtained could facilitate the minimisation of life-cycle cost for the neutralised RC bridges and enhance the functionality of a bridge management system (BMS).

Displacement-based seismic design for buildings

Abstract This paper presents a seismic design method based on displacements rather than force to include inelastic behavior of buildings. By using the substitute structure approach, a rational linear iteration method is proposed where a target displacement is specified and the required design force, member strength and stiffness are obtained. Examples that illustrate a few typical designs and results of parametric studies are also presented. The procedure shown here has been developed for multiple degree‐of‐freedom (MDOF) systems.