Many researches have been performed on concrete with fly ash and bottom ash. However researches on concrete with pond ash (PA) and its application to RC (Reinforced Concrete) structure are limitedly carried out. This paper presents an applicability of PA concrete in construction of real size structure. Referring to the previous study, 2 domestic PA samples with normal performance are selected and 2 replacement ratios (25% and 50%) to fine aggregate are considered for 5 PA concrete structures consisting of column, slab, and wall. In order to evaluate the property of fresh concrete, several tests including air content, slump, and setting time are performed. Using cored out samples from hardened PA concrete structure, tests for strength, resistance to carbonation and chloride penetration are carried out and compared with control samples. Additionally, tests for rebound hardness, drying shrinkage, and hydration heat are performed for PA concrete structure. The test results showed that PA concrete has reasonable strength and durability performances compared to those of normal concrete. Therefore, its potential application to RC structure is promising. The PA aggregate can be more actively used for RC structures with better quality control for content of fly ash, bottom ash, and unburned carbon.
In underground parking lots of apartment housing, the story height is increased by $300{\sim}400mm$ because of various ducts for HVAC. In order to reduce this story height, this study proposed the 'hybrid beam', which is composed of PC beam with embedded steel beam and insitu concrete. The depth of the hybrid beam is reduced by 300 mm and then the steel beam is embedded over the length of reduced depth to compensate for the loss of strength. Then, we performed the large-scale structural tests on 9 specimens and investigated the flexural behavior of the specimens. The parameters of tests were the shape of steel beam section, the length of the reduced depth, the stage of construction, the effects of slab and shear connectors. The test results showed that the specimens, after the insitu concrete has cured, has the flexural capacity which exceeds the required design capacity regardless of other parameters. On the other hand, the specimens of construction stage do not have sufficient strength. Based on these results, it is thought that the proposed hybrid beam with reduced depth is applicable to the underground parking lots of apartment housing as long as the support is placed at construction stage.
The repair of concrete surfaces does not normally take into account structural tolerance for longer service lift and better capabilities of concrete structures. In particular, the repair of surface spelling completes as mortar is applied, which does not display additional structural performances. The use of crimped wire mesh for better construction and fracture resistance, however, expects to have some reinforcement effects. Particularly, it is also expected that the repair of bottom part in structures built between bridges like irrigation structures results in the increase of flexural resistance. Therefore, this study is intended to perform the repair using crimp wire mesh and examine strength depending on the repair section and depth. For this, a slab with 150 mm in depth, 3,000 mm in length and 600 mm in width and total 8 objects to experiment such as upper part, upper whole, bottom part, bottom whole and crimp wire mesh reinforced are manufactured to perform flexural performance. The results of the analysis show that yield strength and failure load increase as the depth of repair materials in the experiment reinforced with crimp wire mesh get bigger. In the same condition, repair of bottom part is able to increase internal force of bending force. Besides, the results show that partial repair of structures under bending force cannot produce flexural performance. Consequently, the repair method with crimp wire mesh results in the increase of flexural resistance.
Han, Sang-Whan;Kee, Seong-Hoon;Kang, Tomas H.K.;Cho, Jong;Lee, Li-Hyung
Journal of the Korea Concrete Institute
/
v.18
no.5
s.95
/
pp.595-602
/
2006
An experimental study was conducted to investigate seismic behaviour of post-tensioned(PT) exterior slab-column connections used for the purpose to resist gravity loads only. For these, 2/3-scale, two PT post-tensioned exterior connections with two different tendon arrangement patterns and one conventional reinforced concrete(RC) exterior connection was tested under quasi-static, uni-directional reversed cyclic loading. During the lateral testing, gravity forces transferred to the column were kept constant to closely simulate a moment to shear ratio of a real building. One of the objectives of this study was to assess the necessity and/or the quantity of bottom bonded reinforcement needed to resist moment reversal which would occur under significant inelastic deformations of the adjacent lateral force resisting systems. The ACI 318 and 352 provisions for structural integrity were applied to provide the bottom reinforcement passing through the column for the specimens. Prior test results were also collected to conduct comparative studies for some design parameters such as the tendon arrangement pattern, the effect of post-tensioning forces and the use of bottom bonded reinforcement. Consequently, the impact of tendon arrangement on the seismic performance of the PT connection, that is lateral drift capacity and ductility, dissipated energy and failure mechanism, was considerable. Moreover, test results showed that the amount of bottom reinforcement specified by ACI 352. 1R-89 was sufficient for resisting positive moments arising from moment reversal under reversed cyclic loads. Shear strength of the tested specimens was more accurately predicted by the shear strength equation(ACI 318) considering the average compressive stress over the concrete($f_{pc}$) due to post-tensioning forces than that without considering $f_{pc}$.
Proceedings of the Korea Concrete Institute Conference
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2008.11a
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pp.9-12
/
2008
The semi-rigid joint is the shape of middle that can supplement the defect of pin joints and accept the good point of rigid joints. Recently, a study on the pin joints is activated in the country, but because the study on semi-rigid joints is not many, this study tried to prove with producing test model of three shape. The test models are rigid joint HI-R, semi-rigid joint HI-S, pin joint HI-P. As a result of the test, respectively HI-R, HI-S, HI-P appeared shear failure of joint, flexure failure of the top fixing, flexure failure of the lower part slipping stair slab, and the maximum strength is measured to 51.74, 51.4, 24.63kN, the stiffness is appeared 1.58, 1.19, 0.37 respectively, The yield strength is respectively kept 44.5, 47.3, 24kN, and ductility ratio is appeared to 3.31, 2.32, 1.54, when is based on KBC code, sag of the acting service load is appeared that HI-P model is over the standard. When is based on distribution of bars strain ratio, HI-S seems similar behavior incipiently, but after the yield, the semi-rigid joint was able to be judged better than pin joint because of the stress allotment of joint internal elements.
A new modified full scale double tee slabs with the length of nib plate - 1,500 mm were suggested, designed, and experimentally evaluated up to the loading of flexural failure. This slabs were composed of the tee section which was same to original PCI double tee and the plate section which was modified in a new shape, and the prestressing force was applied at the bottom of tee section only. This specimens were made from the domestic precast factory. The safety and serviceability of the modified nib plate with the dapped ends were evaluated up to the ultimate flexural strength of tee section. As the experimental loading increased, the flexural crackings developed first in the bottom of the slab and they changed to the increased flexural shear and inclined shear crackings in the nib and dapped portion of the double tees. The suggested modified double tee slabs failed in ductile above the design loading with many evenly distributed flexural crackings. The thickness of nib plate - 250 mm does not show any cracking under the service loading and show several minor flexural cracking up to the ultimate state of tee portion. The proposed specimens were satisfied with the strength and ductility requirements in the design code provisions in the tests. Additional experimental tests are required to reduce the depth and tensile reinforcement of nib plate concrete for the practical use of this system effectively.
A restraint coefficient for creep and dry shrinkage deformation of concrete in a composite section was derived to calculate the residual stress, and an equation for the loss rate of the pre-compression force was proposed. The derived restraint coefficient was computed by using the transformed section properties for the age-adjusted effective modulus of elasticity. The long-term behavior of complicate composite sections could be analyzed easily with the restraint coefficient. The articles of the current design code was examined for PSC and steel composite sections. The dry shrinkage strains of $150 ~ 200$\times$10^{-6}$ for the computations of the statically indeterminate force and the expansion joint could be under-estimated for less restrained sections such as the reinforced concrete. The dry shrinkage strain of $180$\times$10^{-6}$ for the computation of residual stress in the steel composite section was unreasonably less value. The loss rate of 16.3% of the design code for the PSC composite section in this study was conservative for the long-term deformation of the ACI 205 but could not be used safely for that of the Eurocode 2. For pre-compressed concrete slab in the steel composite section, the loss rate of prestressed force with low strength reinforcement was much larger than that with high strength tendon. The loss rate of concrete pre-compression increased, while that of pre-tension decreased due to the restraint of the steel girder.
This study was performed to investigate the compatibility between 4 dentin adhesives and 4 resin luting cements. Dentin adhesives used in this study were All-Bond 2 (Bisco Inc., Schaumbrug, IL, USA), Clearfil SE-Bond (Kuraray Medical Inc, Osaka, Japan), Prompt L-Pop (3M Dental Products, St. Paul, MN, USA), One-Up Bond F (Tokuyama corp., Tokyo, Japan) Resin luting cements used in this study were Choice (Bisco Inc., Schaumbrug, IL, USA), Panavia F (Kuraray Medical Inc, Osaka, Japan), RelyX ARC (3M Dental Products, St. Paul, MN, USA) Bistite II DC (Tokuyama corp., Tokyo, Japan). Combination of each dentin adhesive and corresponding resin cement was made to 16 experimental groups. Flat dentin surfaces was created on mid-coronal dentin of extracted mandibular third molars, then dentin surface was polished with 320-grit silicon carbide abrasive papers. Indirect resin composite block (Tescera, Bisco) was fabricated. Its surface for bonding to tooth was polished with silicon carbide abrasive papers Each dentin adhesive was treated on tooth surface and resin composite overlay were luted with each resin cement. Each bonded specimen was poured in epoxy resin and sectioned occluso-gingivally into 1.0mm thick slab, then further sectioned into $1.0{\times}1.0mm^2$ composite-dentin beams. Microtensile bond strength was tested at a crosshead speed of 1.0mm/min. The data were analysed by one-way ANOVA and Duncan's multiple comparison tests The results of this study were as follows, 2-step self-etching dentin adhesive which has additional bonding resin is more comparison than tests. self-etching dentin adhesive.
Journal of the Korea institute for structural maintenance and inspection
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v.24
no.5
/
pp.111-118
/
2020
The U-shaped composite beam used in this study consist of a reinforced concrete structure, a beam steel structure supporting the slab, a reinforced concrete structure, and a U-shaped steel plate. The U-shaped composite beam was developed for the purpose of using it as a parking lot because it is highly constructible and has low floor height and long span. For the improvement of constructivity, the U-shaped composite beam ends are planned with standardized H-shaped steel and connected directly to the columns, and the middle of the U-shaped composite beam consists of U-shaped steel plates folded in U-shaped form using thin steel plates (t=6) instead of H-shaped steel. In the middle of the composite beam, where U-shaped steel plates are located, the depth of U-shaped beam may be planned to be small so as to satisfy the height limit of the parking lot. It is important to grasp the structural performance according to the change of depth because low beam depth is advantageous for the reduction of the floor height, but it is a inhibitor to the structural behaviors of U-shaped composite beam. In addition, since U-shaped composite beams are a mixture of steel frame structures, reinforced concrete structures and U-shaped steel plates, securing unity has a great influence on securing structural performance. Therefore, in this study, a structural experiment was conducted to understand the structural performance according to the depth change for U-shaped composite beam. A total of three specimens were planned, including two specimens that changed the depth using a criteria specimen planned for a general parking lot. The results of the experiment showed that the specimens who planned the depth greatly had better structural performance such as yield strength, maximum strength, and energy than the standard specimen.
Journal of the Korea institute for structural maintenance and inspection
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v.26
no.6
/
pp.128-138
/
2022
In this study, in order to apply ultra-high-strength concrete beams of 100 MPa or more manufactured by centrifugal molding as the superstructure of the avalanche tunnel, the purpose is to verify the structural safety of the corner rigid joint in which the centrifugal molded beam is integrated with the substructure, which is the negative moment area. A full-size specimen was manufactured, and loading tests and analysis studies were performed. In order to expect the same effect that the maximum moment occurs in the corner joint part of the upper slab end when the standard model of the avalanche tunnel is designed with a load combination according to the specification, a modified cantilever type structural model specimen was manufactured and the corner rigid joint was fixedly connected. A study was performed to determine the performance of the method and the optimal connection construction method. The test results demonstrated that the proposed connection system outperforms others. Despite having differences in joint connection construction type, stable flexural behavior was shown in all the tested specimens. The proposed method also outperformed the behavior of centrifugally formed beams and upper slabs. The behavior of the corner rigid joint analysis model according to the F.E. analysis showed slightly greater stiffness compared to the results of the experiment, but the overall behavior was almost similar. Therefore, there is no structural problem in the construction of the corner rigid joint between the centrifugally formed beam and the wall developed in this study.
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