Thomas H.-K. Kang

Combined half precast concrete slab and post-tensioned slab topping system for basement parking structures

Abstract It is known that the prestressed half PC (precast) slab system has many advantages such as a reduced construction period and use of long-span one-way slab systems over reinforced concrete and half PC slab systems without prestressing. For this reason, prestressed half slabs are commonly used for both residential and basement parking structures in Korea and other countries. The prestressed half PC slab systems currently being used only have the pre-tensioning system only for PC slabs. To ensure better performance of the half PC slab system with larger span-to-depth ratio, a new system using both pre-tensioning and post-tensioning methods is suggested for basement parking structures in this paper. The main purpose of this paper was to analyse the suggested model and verify its safety and serviceability for a given span and a given load. The second purpose is to suggest a preliminary calculation process for the suggested system that satisfies the ACI 318 requirements. A parametric study is conducted in order to find the best and most economic model using four variables: (1) depth of precast concrete; (2) depth of topping concrete; (3) number of pre-tensioned tendons; and (4) number of post-tensioned tendons. The obtained model satisfies the requirements of ACI 318 in terms of working stress design.

Cyclic Testing for Seismic Design Guide of Beam-Column Joints with Closely Spaced Headed Bars

Given the overly strict requirements for clear headed-bar spacing in ACI 318-08 and the lack of headed bar provisions in CEB-FIB MC 90, two approximately 2/3-scale exterior beam-column connection subassemblies were tested under cyclic lateral loading. The tests primarily explored the effect on their seismic performance of using (a) small clear spacings and (b) multiple layers of headed bars in the beam. Also, previous test data were thoroughly analyzed. It was concluded that the clear bar spacing of approximately 2db or the use of two bar layers may be permitted for headed bars anchored in exterior beam-column joints.

Porosimetric features of calcium sulfoaluminate and Portland cement pastes: testing protocols and data analysis

Abstract Investigating pore structure of calcium sulfoaluminate cement paste is significantly important to understand the hydration process of cement, to develop the models that describe the cement paste microstructure, and eventually to improve the properties of the cement paste such as shrinkage compensation and self-stressing. The history, manufacture, and hydration of calcium sulfoaluminate cement are investigated. Two most common experimental protocols, nitrogen sorption and mercury intrusion porosimetry, are systematically summarized with required theories for analysis of porosimetric features of the cement pastes. Both calcium sulfoaluminate and portland cement pastes were tested with a water-to-cement ratio of 0.4, 0.5, and 0.6 using the two test methods. Since the measurement range of pore diameter by the nitrogen sorption porosimetry is relatively narrow (about 0.3–300 nm), the microporous properties of cement paste can be well determined. The mercury intrusion porosimetry is useful to evaluate the porosimetric features of cement pastes including bulk durability due to the wide measurement range of pore diameter (approximately 3 nm–200 μm).

Development of design aid for barrel vault shaped membrane fabric structures

Abstract This study introduces the development of membrane fabric structures as well as the procedure for their design and analysis along with an explanation of the finite element modeling and conditions considered. In addition, a parametric study on regular barrel vault shaped membranes supported between arches is conducted. The following three parameters determine the geometry of this type of membranes: the arch curvature, the width of the panel, and the scale of the arch. Considering these three parameters and the different combinations among them, regular membrane panels are analyzed leading to the development of a design aid for this type of membranes.

An Experimental Study on Flexural Behavior of Steel Fiber Reinforced Concrete Beams Using Recycled Coarse Aggregates

One of the problems of modern society is that the environment of the construction sector is more serious than other industries. However, use of recycled aggregates in the construction sector in order to solve these environmental problems is lower. Given the lack of such effects, the main objective of this experimental study is to investigate flexural behavior (and/or flexural strength) of steel fiber RC beams using recycled aggregates. The main variables are longitudinal steel ratios (=0.45, 0.8, 1.27 and 1.83%) and steel-fiber volume fraction (=0, 0.5, 0.75 and 1%). A total of 16 specimens were tested as a simply supported beam subjected to a two-point load. As a result, specimens failure modes were quite different according to the steel fiber volume fraction. Also, with the addition of more steel fibers, beam crack size and spacing was reduced, and beam ductility was increased.