Korea Concrete Institute
Taiwan Concrete Institute
International Federation for Structural Concrete
The special sessions present recent advances in the design, construction, evaluation, and repair of concrete structures and materials with an emphasis on international perspectives with members from four major concrete institutes around the globe: the American Concrete Institute (ACI), Korea Concrete Institute (KCI), Taiwan Concrete Institute (TCI), and International Federation for Structural Concrete (FIB). Presentations encompass a variety of technical aspects such as the refined analysis and assessment techniques of concrete members, damage detection and mitigation, seismic behavior, durability performance, and repair/strengthening of constructed structures. Both experimental and analytical investigations are of interest. The sessions bring to light state-of-the-art knowledge and provide an opportunity to discuss current challenges and technical demands. Critical information will be provided to those who lead tomorrow’s structural design, construction, evaluation, and repair, including practicing engineers, government officials, and academics.
(1) Analyze the implications of extreme loadings;
(2) Evaluate seismic vulnerability of concrete structures;
(3) Identify the complex collapse mechanism of structural concrete;
(4) Investigate the use of alternative construction materials.
This session has been AIA/ICC approved for 2 CEU/PDH credits.
Maximum Shear Strength of Reinforced Concrete Columns Under Seismic Loading
Presented By: Shyh-Jiann Hwang
Affiliation: National Taiwan University
Description: The maximum shear strength is defined as the crushing of concrete struts prior to the yielding of shear reinforcement. If the amount of transverse reinforcements of the column is sufficient and would not yield due to shear force, the diagonal compression is transmitted between the cracks, which eventually causes the concrete to be crushed producing a brittle shear failure. The limit the maximum shear strength in reinforced concrete columns is to prevent possible sudden shear failure due to over reinforcement. This study conducted experiments on four RC rectangular columns with sufficient amount of transverse reinforcement. Test parameters include the axial load ratio and the amount of longitudinal reinforcement. Shear compression failures with the concrete crushing prior to the yielding of shear reinforcement were observed. Because the transverse reinforcement of column remains elastic during peak load, the diagonal compression of the concrete struts can be transmitted in the direction close to the initial cracking angle. A proposal for determining the maximum shear strength of rectangular columns has been made.
Needs for Standardized Test Methods of Material and Structures under Extreme Loads
Presented By: Jae-Yeol Cho
Affiliation: Seoul National University
Description: Extreme loadings indicate impact loading or extremely low-temperature environments, where material properties or structural behavior mechanisms vary from regular ones. Therefore, the standards and results developed through previous research on static loading or regular environment cannot be applied to extreme situations. Accordingly, a new kind of research focusing on extreme events is necessary to develop design methods. In this area, special experiments, i.e., extreme performance tests should be employed to evaluate the performances of materials and structures under extreme loading. Unlike conventional tests, there is no standardized test method for extreme performance tests. Accordingly, researchers have performed tests on their own method, which makes it difficult to collect, compare, analyze, and utilize test data. In order to solve this issue, Extreme Performance Testing Center is conducting research to standardize extreme performance tests of materials and structures. To be specific, a high-rate material test technique is being developed using split Hopkinson pressure bar and high-speed loading machine. For structural tests, the minimum member size, boundary condition, and measurement technique are covered using gas-guns, drop-weight impact tester, and extreme temperature chamber. It is expected that the advancement of technology in extreme engineering fields can be achieved through the standardized test method.
Seismic Behavior of Reinforced Concrete Frames with Masonry Infill Walls Strengthened by UHPC Shotcrete
Presented By: Chung-Chan Hung
Affiliation: National Cheng Kung University
Description: Reinforced concrete (RC) frames with masonry infill walls are commonly used in seismic regions around the world. Over the years, many RC frames with masonry infill walls collapsed in Taiwan due to their inability to withstand the impact of earthquakes. The objective of the present study was to investigate the effectiveness of ultra-high-performance concrete (UHPC) for enhancing the collapse-resistant capacity of RC frames with masonry infill walls. For this purpose, three full-scale RC frames with masonry infill walls, including a specimen without retrofitting and two specimens retrofitted with UHPC shotcrete, were constructed and tested under lateral displacement reversals. The experimental variable was the use of steel bar mesh in the UHPC retrofitting layer. The seismic behavior of the structures was extensively evaluated using the performance parameters including the initial stiffness, yield and peak strengths, ductility, damage pattern, strength and stiffness attenuation, and energy dissipation capacity. In addition to the experimental study, numerical models were proposed to evaluate the seismic behavior of the tested structures.
Multi-Linear Model for Beam-Column Joints under Progressive Collapse
Presented By: Hyeon Jong Hwang
Affiliation: Konkuk University
Description: When local damage occurs due to unexpected events, compressive arch action (CAA) and catenary action (CTA) increase the progressive collapse resistance beyond the conventional plastic hinge mechanism. To estimate structural performance, large-scale structural tests are generally time-consuming and laborious, while finite element analysis requires in-depth professional knowledge and proficient modeling skills. In the present study, a simplified analysis model was developed to evaluate the progressive collapse resistance of moment sub-frames after the removal of a penultimate column. To estimate the load-carrying capacity and corresponding deformation at each mechanism, the effects of boundary condition, and the geometric and material properties of the beam section on the structural performance were considered. The validity of the proposed method was verified by comparison with the existing test results of moment sub-frames under progressive collapse. Further, a parametric study was performed to investigate the effects of concrete strength, reinforcement ratio, beam section size, and beam span on the progressive collapse resistance of the substructure. The analysis results showed that increasing the beam depth or beam top bar ratio significantly increased the progressive collapse resistance.
Effect of Key-Design Parameters on the Flexural Behavior of CFFT-Rectangular Beams Post-Tensioned with Steel Tendons
Presented By: Radhouane Masmoudi
Affiliation: University of Sherbrooke
Description: This talk presents the results of a research project to study the flexural behavior of rectangular CFFT beams post-tensioned with unbonded steel tendons. Full-size beams with internal steel bars were tested, including twelve PT CFFTs, two PT concrete beams, and one non-PT CFFT for comparison. The investigated parameters are i) GFRP tube thickness ranged from 6.0 mm to 12.3 mm; ii) Tube fiber structural laminate; iii) Tube confinement versus steel stirrups; iv) Number of prestressing tendons and level of prestressing; v) Concrete compressive strength [(normal and high strength concrete (NSC and HSC)]; vi) Total reinforcement index; vii) Attaching a thin Carbon FRP-laminated embedded in tension flange and its ratio; and viii) Loading scheme (static and cyclic). An analytical study was conducted to develop a new model to predict the ultimate strength of prestressed CFFT members. The model is based on strain compatibility and force equilibrium, which account for the material constitutive relationships for FRP tube laminates, steel strands, and non-linearity of concrete. The accuracy of the proposed model is also verified against the experimental results. Finally, a new design equation, as an extension to AASHTO (2012) equation, is also established based on the test results to predict the ultimate flexural capacity of the tested beams.
Noncontact Lap Splices of 600MPa (87ksi) Reinforcing Bars in Slabs
Presented By: Sung-Chul Chun
Affiliation: Incheon National University
Description: Lap splices in reinforced concrete structures typically consist of bars overlapped and placed in contact with each other. In the cases of walls or slabs with minimum reinforcement, longitudinal bars are widely spaced and noncontact lap splices of the bars are commonly used. In ACI 318, bars spliced by noncontact lap splices shall not be spaced transversely farther apart than the lesser of one-fifth the required lap splice length and 150 mm (6 in.) to prevent the cracks between the spliced bars. The 150 mm (6 in.) maximum spacing is added because most research was conducted with reinforcement within this spacing. Four-point flexural tests on twenty-two slabs reinforced with 600MPa (87ksi) yield strength bars were conducted. The main variable is a spacing between sliced bars; contact, 150 mm (6 in.), and 225 mm (9 in.). The other variables include the bar diameters, concrete strength, and transverse reinforcement amount. Test results shows that the spacing between spliced bars did not affect the structural behavior and strength of the slabs except cracking patterns. Obviously, as the spacing increased, the cracks to follow a zigzag line increased in tension surface. However, the maximum load, load-deflection relation, and developed bar stress of the slabs that had the same design parameters except the spacing, were almost the same. The developed bar stresses have been compared with the predictions by Orangun et al.'s and ACI 408 equations. Moreover, a new strut-and-tie model has been constructed for the noncontact lap splice to explain the test results. This presentation will show that the noncontact lap splice has the same structural characteristics of the contact slice.