• Steel and Composite Structures
• /
• v.21 no.2
• /
• pp.267-287
• /
• 2016

The seismic performance of the ordinary steel reinforced concrete (SRC) columns has no significant improvement compared to the reinforced concrete (RC) columns mainly because I, H or core cross-shaped steel cannot provide sufficient confinement for core concrete. Two improved SRC columns by constructing with new-type shaped steel were put forward on this background, and they were named as enlarging cross-shaped steel and diagonal cross-shaped steel for short. The seismic behavior and carrying capacity of new-type SRC columns have been researched theoretically and experimentally, while the shear behavior remains unclear when the new-type columns are joined onto SRC beams. This paper presents an experimental study to investigate the shear capacity of new-type SRC joints. For this purpose, four new-type and one ordinary SRC joints under low reversed cyclic loading were tested, and the failure patterns, load-displacement hysteretic curves, joint shear deformation and steel strain were also observed. The ultimate shear force of joint specimens was calculated according to the beam-end counterforce, and effects of steel shape, load angel and structural measures on shear capacity of joints were analyzed. The test results indicate that: (1) the new-type SRC joints display shear failure pattern and has higher shear capacity than the ordinary one; (2) the oblique specimens have good bearing capacity if designed reasonably; and (3) the two proposed construction measures have little effect on the shear capacity of SRC joints embedded with diagonal cross-shaped steel. Based on the mechanism observed from the test, the formulas for calculating ultimate shear capacity considering the main factors (steel web, stirrup and axial compression ratio) were derived, and the calculated results agreed well with the experimental and simulated data.

• Journal of the Korean Geotechnical Society
• /
• v.34 no.3
• /
• pp.67-75
• /
• 2018

In this study, we developed a micropile equipped with ground fixing wedge device which is able to ensure the bearing capacity early before grouting by expanding the tip and exerting the tip surface friction while compressing and expanding the tip of the micropile during loading. The purpose of this study is to verify the applicability of the developed micropile to the ground with various kinds of strength and to compare its characteristics with those of the simple tip expansion micropile. A new test system including a model soil box which can measure the tip resistance and the tip skin friction separately was devised. The loading test was carried out according to the changes of the ground strength and the tip cross section using the devised test systems. As a result of the test, it was found that the developed micropile increased the tip skin friction due to the wedge horizontal force as the soil strength increased and could be applied more effectively to the ground with the strength not lower than the strength of the weathered rock. In addition, it was found that additional bearing capacity could be obtained due to the tip cross section expansion and the wedge horizontal force exertion even in the ground with the strength below the weathered rock strength.

• Journal of the Korea Concrete Institute
• /
• v.25 no.2
• /
• pp.217-224
• /
• 2013

Design provisions for the development length of headed bars in ACI 318-08 include concrete compressive strength and yield strength of headed bars as design parameters but do not consider the effects of transvers reinforcement. In addition, they have very strict limitation for clear spacing and material strengths because these provisions were developed based on limited tests. In this study, splice tests using SD600 headed bars with $2d_b$ clear spacing and transverse reinforcement were conducted. Test results show that unconfined specimens failed due to prying action and bottom cover concrete prematurely spalled. The contribution of head bearing on the anchorage strength is only 15% on average implying that unconfined specimens failed before the head bearing was not sufficiently developed. Confined specimens with stirrups placed along whole splice length have enhanced strengths in bearing as well as bond because the stirrups prevented prying action and improved bond capacity. Bond failure occurred in locally confined specimens where stirrups were placed only at the ends of splice length. The stirrups at ends of splice lengths can prevent prying action but the bond capacity did not increase. From regression analysis of test results, an equation to predict anchorage strength of headed bars was developed. The proposed equation consists of bond and bearing contributions and includes transverse reinforcement index. The average ratio of tests to predictions is 1.0 with coefficient of variation of 6%.

• Steel and Composite Structures
• /
• v.22 no.6
• /
• pp.1337-1358
• /
• 2016

The current study focuses on the assessment and interface response of reinforced concrete elements with composite materials (carbon fiber reinforced polymers-CFRPs, glass fiber reinforced polymers-GFRPs, textile reinforced mortars-TRM's, near surface mounted bars-NSMs). A description of the transfer mechanisms from concrete elements to the strengthening materials is conducted through analytical models based on failure modes: plate end interfacial debonding and intermediate flexural crack induced interfacial debonding. A database of 55 in total reinforced concrete columns (scale 1:1) is assembled containing elements rehabilitated with various techniques (29 wrapped with CFRP's, 5 wrapped with GFRP's, 4 containing NSM and 4 strengthened with TRM). The failure modes are discussed together with the performance level of each technique as well as the efficiency level in terms of ductility and bearing/ bending capacity. The analytical models' results are in acceptable agreement with the experimental data and can predict the failure modes. Despite the heterogeneity of the elements contained in the aforementioned database the results are of high interest and point out the need to incorporate the analytical expressions in design codes in order to predict the failure mechanisms and the limit states of bearing capacities of each technique.

• Journal of the Korean Geotechnical Society
• /
• v.35 no.10
• /
• pp.47-66
• /
• 2019

A parametric numerical analysis according to diameter, length, and N values of soil was conducted for the PHC pile socketed into weathered rock through sandy soil layers. In the numerical analysis, the Mohr-Coulomb model was applied to PHC pile and soils, and the contacted phases among the pile-soil-cement paste were modeled as interfaces with a virtual thickness. The parametric numerical analyses for 10 kinds of pile diameters were executed to obtain the load-settlement relationship and the axial load distribution according to N-values. The load-settlement curves were obtained for each load such as total load, total skin friction, skin friction of the sandy soil layer, skin friction of the weathered rock layer and end bearing resistance of the weathered rock. As a result of analysis of various load levels from the load-settlement curves, the settlements corresponding to the inflection point of each curve were appeared as about 5~7% of each pile diameter and were estimated conservatively as 5% of each pile diameter. The load at the inflection point was defined as the mobilized bearing capacity ($Q_m$) and it was used in analyses of pile bearing capacity. And SRF was appeared above average 70%, irrespective of diameter, embedment length of pile and N value of sandy soil layer. Also, skin frictional resistance of sandy soil layers was evaluated above average 80% of total skin frictional resistance. These results can be used in calculating the bearing capacity of prebored PHC pile, and also be utilized in developing the bearing capacity prediction method and chart for the prebored PHC pile socketed into weathered rock through sandy soil layers.

• Journal of the Korean Geosynthetics Society
• /
• v.16 no.2
• /
• pp.67-77
• /
• 2017

This study analyzes behavior of bearing capacity of open-ended pipe pile from laboratory experiment results. Unlike the conventional pipe piles, cone penetration is implemented into the inside of the pipe pile. During the cone penetration, cone driving energy helps densification of plugged soils and soils below the pile end. Sand pluviator was used to obtain homogeneous soil layers. Two kinds of piles with different pile outer surface roughness were prepared, and two different drop heights of pile driving were applied. Eight experimental cases varying pile outer surface roughness, pile driving energy for conventional and cone penetration implemented piles were conducted. From the experiments, ultimate load of the pile increased approximately by 70% for increased pile driving height, and it increased by 21% for rougher surface pile. When cone penetration is implemented, the ultimate load increased by 40% in average.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.29 no.2A
• /
• pp.109-118
• /
• 2009

A new bridge system described in this paper uses concrete-filled steel tube (CFT) girders as a replacement for conventional girders. Experimental investigations were carried out to comprehend the flexural behavior of CFT girder. Specimens were manufactured considering several parameters such as the strength of filling material, the eventual presence and number of inner shear connectors to evaluate the bending bearing capacity of CFT girder. The experimental investigation consisted of designing and constructing a test specimen and loading it to collapse in bending to check the applicability of the system. Test results showed that concrete filled steel tube girders have good ductility and maintain their strength up to the end of the loading. The stiffening effect of the ㄱ-shaped perfobond rib is determined to contribute relatively to the increase of the bending bearing capacity.

• Journal of the Korean GEO-environmental Society
• /
• v.18 no.7
• /
• pp.37-47
• /
• 2017

In this study, a series of full-scale field tests on prebored and precast steel pipe piles and the corresponding numerical analysis have been conducted in order to study the characteristics of pile load-settlement relations and shear stress transfer at the pile-soil interface. Dynamic pile load tests (EOID and restrike) have been performed on the piles and the estimated design pile loads from EOID and restrike tests were analysed. Class-A type numerical analyses conducted prior to the pile loading tests were 56~105%, 65~121% and 38~142% respectively of those obtained from static load tests. In addition, design loads estimated from the restrike tests indicate increases of 12~60% compared to those estimated in the EOID tests. The EOID tests show large end bearing capacity while the restrike tests demonstrate increased skin friction. When impact energy is insufficient during the restrike tests, the end bearing capacity may be underestimated. It has been found that total pile capacity would be reasonably estimated if skin friction from the restrike tests and end bearing capacity from the EOID are combined. The load-settlement relation measured from the static pile load tests and estimated from the numerical modelling is in general agreement until yielding occurs, after which results from the numerical analyses substantially deviated away from those obtained from the static load tests. The measured pile behaviour from the static load tests shows somewhat similar behaviour of perfectly-elastic plastic materials after yielding with a small increase in the pile load, while the numerical analyses demonstrates a gradual increase in the pile load associated with strain hardening approaching ultimate pile load. It has been discussed that the load-settlement relation mainly depends upon the stiffness of the ground, whilst the shear transfer mechanism depends on shear strength parameters.

• Journal of the Korea Concrete Institute
• /
• v.21 no.4
• /
• pp.389-400
• /
• 2009

A compression lap splice can be calculated longer than a tension lap splice in high strength concrete according to current design codes. Including effects of transverse reinforcement, a compression splice becomes much longer than a tension splice. Effects of transverse reinforcement and bar size on strength and behavior of compression lap splice, which always exist in actual structures, have been investigated through experimental study of column tests with concrete strength of 40 and 60 MPa. The results of the tests with bar diameters of 22 and 29 mm show that there is no size effect of bar diameter on compression lap splice. Bond strength of small bar diameter may increase. However, large diameters of re-bars are used in compression member and the size effect of re-bars does not have to be considered in compression lap splice. Confined specimens have twice of calculated strengths by current design codes. New design equations for the compression lap splice including the effects of transverse reinforcement are required for practical purpose of ultra-high strength concrete. End bearing is enhanced by transverse reinforcement placed at ends of splice not by transverse reinforcement within splice length. As more transverse reinforcement are placed, the stresses developed by bond linearly increase. The transverse reinforcements at ends of splice a little improve the strength by bond. Because the stresses developed by bond in compression splice with transverse reinforcement are nearly identical to or less than those in tension splice with same transverse reinforcement, strength increment of compression splice is attributed to end bearing only.

• Journal of the Korean Geotechnical Society
• /
• v.34 no.6
• /
• pp.17-24
• /
• 2018

In this study, static load test and dynamic load test were performed to evaluate pile-filling material (ZA-Soil) of soil-cement injected precast pile method which was developed by using the ash of circulating fluidized boiler as a stimulant for alkali activation reaction of blast furnace slag. As a result of the static load test, the allowable bearing capacity of pile was 1,350 kN, which was the same as the result of using ordinary portland cement. And total settlement was 6.97 mm, and net settlement was 1.48 mm. These are similar to the total settlement, 7.825 mm, and net settlement, 2.005 mm of ordinary portland cement. As a result of the dynamic load test and CAPWAP analysis, the skin friction was 375.0 kN, the end bearing capacity was 3,045.9 kN, and the allowable bearing capacity was 1,368.36 kN. These results are similar to the results of using ordinary portland cement as pile-filling material.