Seismic Behavior of Hybrid Coupled Wall System

Reinforced concrete (RC) couple wall systems, where RC beams couple two or more RC walls in series, are frequently used in high-rise buildings. Generally, coupling beams are made of RC materials. Steel coupling beam is an alternative for RC coupling beam which has a complex and and unefficient detailing construction. This paper presents a study on the use of Hybrid Coupled Wall System (HCWS) in seismic resistant high-rise RC structures. In the study, 25 storey office buildings with three types of coupling beams and three types of walls distributed over the height of the structure and located in a region with high seismicity are designed. Applying a performance-based design approach, this study developed an efficient design for RC structures having Coupling Ratio (CR) values 64.55% and affect the behavior of the wall pier in the upper region of the structure where widespread plastification and earlier crushing failure happen. Based on this findings, steel coupling beams can be used as an alternative with statisfying all performance criteria and perform at Life Safety(LS)

Experimental Study of Confined Low-, Medium- and High-Strength Concrete Subjected to Concentric Compression

An  experimental  study  of  23  low-,  medium-  and  high-strengthconcrete  columns is presented in this paper. Square-confined concrete columns without  longitudinal  reinforcement  were  designed,  and  tested  under  concentric axial  compression.  The  columns  were  made  of  concrete  with  a  compressive strength ranging between 30 MPa and 70 MPa. The test parameters in the study are  concrete  compressive  strengths  and  confining  steel  properties,  i.e.  spacing, volumetric  ratios  and  configurations.  The  effects  of  these  parameters  on  the strength  and  ductility  of  square-confined  concrete  were  evaluated.  Of  the specimens tested in this study, the columns made with higher-strength concrete produced less strength  enhancement and ductility than those with lower-strength concrete.  The  steel  configurations  were  found  to  have  an  important  role  in governing  the  strength  and  ductility  of  the  confined  high-strength  concrete. Moreover,  several  models  of  strength  enhancement  for  confined  concrete available  in  the  literature  turned  out  to  be  quite  accurate  in  predicting  the experimental results

Force Transfer Mechanism of Headed Anchorage Bar in Exterior Beam Column Joint with Finite Element Method and Strut and Tie Model

In structural concrete, the provisions for anchorage of straight bars and hooks sometimes present detailing problems due to the long development lengths and large bend diameters that are required. Occasionally, the requirements for straight bar anchorage and lap splices cannot be provided within the available dimensions of elements. Hooked bars can be used to shorten anchorage length, but in many cases, the bend of the hook will not fit within the dimensions of a member or the hooks create congestion and make an element difficult to construct. This congestion may lead to high fabrication effort needed and poor concrete placement, resulting in decrease of concrete quality at the joints. An alternative is the use of headed anchorage bar, which allows for extremely small development lengths, that can reduce congestion without compromising the integrity of the structure. As a result, designing and detailing the structure are made easier and more efficient. Headed bars are formed by the attachment of a plate or the forging of an upset bearing surface at the end of a straight reinforcing bar. Such bars are anchored by a combination of bond along the straight bar length and direct bearing at the head. This papers presents strut and tie models explaining force transfer mechanism of headed anchorage bar in exterior beam-column joint under monotonic loads. The proposed model is derived from beam-column joint specimen which have been tested experimentally. Stress and strain generated by modeling the beam column joint with finite element-based program, ATENA 3D. The result of the analysis explaining the behavior of headed anchorage bar is CCT nodes (compression-compression-tension). The model is consists of a strut with the nodal zone at the head for head bearing and a fan-shaped stress field for bond stresses along the development length

Seismic Performances of High Rise R/C Frame Structures Reinforced with High Strength Rebars

Construction of high rise buildings as supporting infrastructures for economic growth has increased significantly in numbers in many big cities around the world. In Indonesia, most of the high-rise buildings constructed are made of reinforced concrete structures. In principles, the use of high-strength concrete, coupled with high strength rebars for high rise r/c buildings will result in more efficient and more constructible r/c constructions. However, in Indonesia, the use of high strength rebars for seismic-resistant r/c buildings is still prohibited. SNI 2847:2013 Section 21 specifies that the yield strength for reinforcing bars used in structural elements of special moment resisting frames is limited to 420 MPa. This provision is meant to limit higher shear and higher bond demand in the structural elements assigned to dissipate seismic energy. This paper presents a study on the use of high strength rebars in seismic resistant r/c buildings. In the study, 20 story buildings located in a region with high seismicity are designed. Two types of rebars are used, i.e., those with the yield strength of 550 MPa and of 690 MPa. The building structures are designed as the special moment resisting frame. The seismic performances of the buildings are then investigated by performing non-linear time history analysis. Seven pairs of scaled ground motions are used for the analysis. From this analysis, the failure mechanism of r/c buildings reinforced with 550 MPa yield strength is governed by beam mechanism, while the buildings reinforced with 690MPa yield strength rebars shows failure mechanism dominated by story mechanism. Globally, the performance levels of the buildings are within the zone of Damage Control (i.e., between immediate occupancy and life safety). Based on the findings, some recommendations are proposed for the use of high strength rebars in the design of seismic resistant high rise r/c buildings

Experimental Study of Confined Low-, Medium- and High-Strength Concrete Subjected to Concentric Compression

An experimental study of 23 low-, medium- and high-strengthconcrete columns is presented in this paper. Square-confined concrete columns without longitudinal reinforcement were designed, and tested under concentric axial compression. The columns were made of concrete with a compressive strength ranging between 30 MPa and 70 MPa. The test parameters in the study are concrete compressive strengths and confining steel properties, i.e. spacing, volumetric ratios and configurations. The effects of these parameters on the strength and ductility of square-confined concrete were evaluated. Of the specimens tested in this study, the columns made with higher-strength concrete produced less strength enhancement and ductility than those with lower-strength concrete. The steel configurations were found to have an important role in governing the strength and ductility of the confined high-strength concrete. Moreover, several models of strength enhancement for confined concrete available in the literature turned out to be quite accurate in predicting the experimental results

PERILAKU DAKTILITAS KOLOM BETON BERTULANG DENGAN CINCIN BAJA SEBAGAI EXTERNAL CONFINEMENT

Column is a very important load bearing structural element. When column fails, it does not only cause the collapse of the story where the column exists but may catastrophically disintegrate the overall structure. In this manner, first story column should possess sufficient ductility by which the structure should be able to deforms with large lateral drift, hence, the life safety extendsway beam mechanism develops. One way to enhance concrete ductility is by using confinement as it eenhance the stress and strain of concrete. This study proposes new alternative of confining concrete column by means of external steel ring. Steel ring is employed solely as an external confinement. Despite the fact that the steel ring does not act as external reinforcement, however, it improves the ductility, enhances the column capacity, maintains the cross-sectional area of concrete from premature spalling, and strengthens the columns. The preliminary study employed concrete cylinder confined with steel rings. The cylinder was 300 mm in height and 155 mm in diameter subjected to uniaxial load according to SNI 03-1974-1990. The study was conducted to investigate the effect of confinement on the mechanical properties of concrete. The thickness of steel ring was constant at 2.4 mm. Variation of steel ring volumetric ratio is based on variations in width (28, 45, and 73 mm) and the clearances between the steel ring (90, 47, and 25 mm). The results were used as the basis to predict the the capacity and ductility of the reinforced concrete (RC) columns confined with steel rings under cyclic loading. Eventually, half scale laboratory test was performed to determine the effects of the external confinement. The test specimen was a RC circular column with height of 1710 mm and diameter of 260 mm. The thickness of steel ring was 6.3 mm, the width of 50 mm and clearances between the steel ring was 80 mm (volumetric ratio of steel rings was 1.86%). The specimen was subjected to a constant axial load and lateral cyclic in accordance to ACI 374.2R-13. Three RC circular columns specimens were employed in the investigation. The first specimen was unconfined column (K0-0,4) and the second specimen was column confined by steel rings (KT-0.4). Both were under constant axial load with axial load ratio of 0,4P . The third specimen was a column confined by steel ring (KT-0.6) subjected to a constant axial load with axial load ratio of 0,6P 0 0 . The preliminary study clearly demonstrates that the steel ring is effectively confine the concrete, as its stress and strain increases compared to the unconfined concrete. With steel rings volumetric ratio range was 1.25 to 2.28%, it is found that the confinement of concrete may be attributed as high confinement level as the effective confinement index reaches 21.99 while the concrete strength reaches 2.29. The half scale RC circular columns confined with steel ring exhibit higher ductility, load carrying capacity and resistance than the unconfined column. The displacement ductility index of the test specimen K0-0,4; KT-0,4; and KT-0,6 column are 6.33; 8.38; and 6.82, respectively, while the curvature ductility index of specimen KT0-0,4; KT0,4; and KT-0,6 column are 7.72; 9.72; and 8.23 respectively. Keywords: column, ductility, external confinement, steel ring

NON-LINIER COMPRESSION STRESS-STRAIN CURVE MODEL FOR HARDWOOD

Non-linier compression stress-strain relationship was derived from experimental investigation of 144 small clear specimens of three Indonesian hardwood species, namely Acacia, Meranti and Kruing. Both compression parallel to the grain and compression perpendicular to the grain were tested. The stress-strain curve consists of linier-elastic line until proportional limit and bi-linier curve. Stress-strain curve parameters for compression parallel to the grain, such as elastic modulus, post-elastic modulus, proportional limit, ultimate stress and post-elastic strain limit were derived based on the specific gravity. And also stress-strain curve parameters for compression perpendicular to the grain, such as elastic modulus, post-elastic modulus and proportional limit were derived based on the specific gravity and the angle between stress direction and tangential axis direction. Compression strength perpendicular to the grain in tangential direction was found much lower than compression strength perpendicular to the grain in radial direction

Pengaruh Pemodelan Zona Terkekang Terhadap Prediksi Hubungan Momen-Kurvatur Kolom Persegi Beton Mutu Tinggi

. This paper studies one aspect of confinement modeling of high strength concrete square columns subjected to axially eccentric compression. Confined zone models were studied to evaluate their effect on the analytical prediction of strength and ductility of high strength concrete square columns. Several models of confined zones found in literatures were discussed to observe their characteristics and sensitivity. Based on the findings, a computer program MOKUR2D was developed. In the program, confined zone in reinforced concrete columns can be modeled with three different approaches, i.e. conventional models (using a coefficient of effective confinement), models with unconfined arching zone, or models with three zones of confinement. A comparative study using the program was later carried out on 4 high-strength concrete square columns tested by Sheikh and Bayrak [1998]. The cross-section size of all columns was 305 x 305 mm. All columns were reinforced with 8 bars of 19.5 mm diameter, uniformly distributed around the core perimeter. Yield strength of the rebars was 454 MPa. Two types of ties configuration ties were used with volumetric ratio varying from 1.68 percent to 5.12 percent. The spacing of the ties was from 90 mm to 108 mm. From the study, it was found that the conventional model is able to produce a fairly good estimate of test results. The best estimate of test results is given by the model with three zones of confinement in which the arching zoneis assigned with 50% of full confinement

PENGARUH PEMBERIAN KEKANGAN PADA ZONA TEKAN TERHADAP PENINGKATAN DAKTILITAS BALOK DI LOKASI SENDI PLASTIS AKIBAT BEBAN MONOTONIK DAN SIKLIK

Plastic hinge regions of beam needs special attention, especially in the face of the column while receiving sizeable negative moment by both gravity and the added due to earthquake load. When an earthquake, the compression zone of beam’s section must hold the negative moments and great transverse force while usually compression concrete area is very small so prone to collapse. In this research it intended a more ductile structure elements in the plastic hinge region of beam by providing confinement in compression zone of beam’s section. An experimental investigation was conducted to examine the effect of confinement in the compression zone beam’s section in the plastic hinge that subjected to monotonic and cyclic loading. Six beam specimen with stub that describes the end of the beam – columns joint were prepared. Four specimens were given additional confinement in the compression zone in form of hoops or cross-ties, while the others were made as a beam without additional confinement as a reference. Beams specimen were designed with the greater tensile reinforcement ratio so that it has compressive larger areas of concrete and effective for restraint. An experimental parameters such as an additional form of confinement in a compression zone beam’s section and type of loading given on beam specimens were evaluated and comparisson to ductility, load capacity, energy disipation, and to the pattern of cracks that occur both on beam with additional / without confinement. Test results indicate that presence of confinement in compression zone beam’s section is able to improve the beam’s ductility of displacement and curvature ductility when subjected to monotonic and cyclic loading with an increase of 10 to 100 percent. The existence of confinement in the compression zone beam’s section also increase energy dissipation of beam significantly ranging two until six times energy dissipation of beam without confinement in compression zone. However, confinement in a compression zone beam’s section little influence on the increase in load capacity or the moment capacity when given monotonic and cyclic loading with of below 10 percent. Tests also showed that the area of the beam plastic hinge area damage on all specimens ranged 2/3h to 3/2h from the end of beam - column face. Key word : Confinement, compression zone, ductility, monotonic, cycli

Strength Enhancement, Ductility, and Confinement Effectiveness Index of Fly Ash-based Geopolymer Concrete Square Columns

Geopolymer concrete is an environmentally friendly construction material that has the potential to be applied in building structures. It is important to understand the structural behavior of geopolymer concrete. This paper presents an experimental investigation into the performance of structural elements of geopolymer concrete under concentric axial loads. The specimens were twelve square columns with a size of 170 x 170 mm and a height of 480 mm. The study variables were the tie spacing and the compressive strength of unconfined geopolymer concrete (f’c). The test results showed that the increase in f'cc was not as significant as the increase in unconfined concrete compressive strength (f'c). The value of strength enhancement (K) tended to decrease. The column ductility (m) and confinement effectiveness index (Ic) had optimum values. The effect of increasing the tie spacing (s) decreased the K, Ic, and m values of the column. The proposed f’cc formulation for geopolymer concrete is compatible