Ultra High Strength Concrete Column Research Articles

Stiffness-based stress–strain model of FRP-confined high-strength and ultra-high strength concrete column with various corner radii

This study introduces a unified design-oriented stress–strain model tailored for fiber-reinforced polymer (FRP)-confined high-strength concrete (HSC) with diverse cross-sectional shapes. The proposed stress–strain model incorporates more suitable mathematical forms, incorporating post-peak axial stiffnesses as crucial parameters, thereby enabling the model to accurately capture the three types of post-peak stress–strain behavior observed in FRP-confined HSC: strain-hardening, strain softening, and strain softening recovering to strain hardening. This variation in post-peak axial stiffness arises due to insufficient FRP confinement at the initial peak strength point, as well as changes in the confinement stiffness ratio stemming from the altered dilation behavior of FRP-confined HSC during the post-peak stage. To address the nonuniform effects of FRP confinement, the concept of effective confinement rigidity was defined, unifying the behavior of FRP-confined circular and square HSC. Additionally, the model incorporates the ultimate condition and the characteristic point on the post-peak branch, representing the change in FRP confinement stiffness, to establish the stress–strain model for FRP-confined HSC. The model parameters were evaluated using available experimental results, and the stress–strain curves derived from the proposed model were compared with existing models in the literature, revealing the proposed model's accuracy and rationality.

Structural Behavior of Ultra-High Strength Concrete Columns Reinforced with Basalt Bars Under Axial Loading

The axial compressive behavior of Ultra-High Strength Concrete (UHPC) columns reinforced with basalt bars was investigated in this work. Only a few research projects have used basalt Reinforced Concrete Columns. Under axial stress, 12 columns of 150 × 150 mm in cross section and 1200 mm in height manufactured of M120 grade UHPC, incorporating glass powder lime powder, were tested. The primary characteristics investigated in this study were axial load capacity, axial deformation, failure pattern, ductility, and stiffness. The findings of the experimental tests revealed that the ultimate loads and behavior of UHPCC reinforced with BFRP were superior to concrete columns strengthened with steel reinforcement. When compared to steel RC columns, basalt RC columns carry about 90% of the axial load. Moreover, the BFRP bar tensile strength was 2.5 greater than reinforcing steel yield strength and 1.79 times larger than that of bar. The Ansys software-based analytical analysis assisted in predicting the eventual carrying capacity of UHPC columns. The agreement among the experimental and NLFE ultimate load is around 92.2%, with a standard deviation of 0.005 and a coefficient of variation of 0.00002. The nonlinear BFRP–UHPC columns’ structural performance was adequately predicted by the finite element analysis. In addition, equations are employed to forecast the strength of confined concrete. Equation 4 merely produced improved forecasts, it aids in comparing the outcomes of analytical and experimental tests. Results of this study indicated that the UHPC-columns reinforced with BFRP bars offer potential economic and environmental advantages as compared to traditional RC columns.

New model for confinement of reinforced concrete columns with an ultra-high strength close to 200 MPa

The objective of this work is to develop a new confinement model for ultra-high strength concrete columns confined by transverse reinforcement. First, the mechanism of confinement with transverse reinforcement of square and rectangular section columns has been described. In this context, the existing peak strength and corresponding strain of the stress-strain models, with normal strength (NSC) and high strength (HSC) are selected. Next, the assembled database covering 300 existing experimental data in the literature with an unconfined compressive strength ranging between 20 MPa and 200 MPa is exposed. In order to evaluate the performance of the existing confinement models, three statistical indicators were used, namely: the coefficient of determination (R2), root mean square error (RMSE) and standard deviation (SD). Afterward, the performance of 20 existing confinement models was implemented. According to this study, the proposed peak strength concrete and the corresponding axial strain showed a good performance compared with the 20 selected models. In addition, the expressions of the proposed models are simple and easy to use for design applications.

Hysteretic model of SRUHSC column and SRC beam joints considering damage effects

This paper focuses on developing a hysteretic model of steel reinforced ultra high strength concrete column and steel reinforced concrete beam joint. Characteristics of the hysteretic curve from twelve specimens under cyclic loading were analyzed in terms of damage pattern, residual deformation, loop unloading stiffness deterioration, relative unloading stiffness deterioration and strength degradation. Methods to quantify seismic damage and attenuation coefficient were presented. The proposed methods consider number of loading cycles and controlled displacements which cause seismic damage. The experimental skeleton curve is simplified as a trilinear model, where calculated attenuation coefficient is used to obtain deteriorated stiffness of every segment, deteriorated unloading stiffness, and degraded strength in the hysteretic model. The proposed hysteretic model considering damage effects can describe well the characteristics of experimental hysteretic curves.

Enhancing the performance of UHSC columns intersected by weaker slabs

This paper presents strategies for enhancing the transmission of ultra-high-strength concrete (UHSC) column loads through normal-strength concrete (NSC) slabs in the joint of slab-column connections. Parameters of the investigation were the ratio of column concrete strength to slab concrete strength (fcc′/fcs′), as well as the placement of steel fiber-reinforced concrete, and the installations of high-strength dowel bars and special structural steel inserts in the weak slab joint. The beneficial effects of using high-strength dowel bars and high-strength structural steel inserts on the ability to transmit axial loads from the UHSC columns through the weaker slabs were demonstrated. The benefits of placing steel fiber-reinforced concrete in the joint are not as significant as the additional high-strength steel reinforcement. Predictions of the effective concrete strengths using current code approaches and using equations proposed in the literature were compared to the experimental results. The results indicate that the design approach in the CSA Standard (CSA A23.3-14) and the method proposed by Kayani (1992), which is based on the a data fitting approach, provide reasonable lower bound predictions of the effective strength for the UHSC columns with weaker slab layers.

Enhancing the confinement of ultra-high-strength concrete columns using headed crossties

This study investigates the influence of headed crossties on the confinement of 200MPa ultra-high-strength concrete (UHSC) columns. A Total of six UHSC columns confined by headed crossties (deformed reinforcing bars with heads welded on both ends) and seismic crossties, detailed with 90° bend anchorages alternated end to end, were constructed and tested under pure axial load. The amount and yield strength of transverse reinforcement were varied to determine the efficiency of headed crossties on the confinement of the UHSC columns. The columns with seismic crossties exhibited some loss in confinement due to the loss of anchorage of the 90° hooks that opened up before significant yielding of the crossties could occur. The relatively small heads used are capable of developing the yield force of high-strength transverse reinforcement in the UHSC columns. The use of high-strength headed crossties resulted in improved confinement compared to columns with high-strength seismic crossties resulting in improved post-peak performance of UHSC columns. A prediction model that accounts for the additional confinement pressure due to the bearing of the heads, brittle cover spalling and the stress-strain relationship of UHSC was used to predict the axial load-strain behavior of the UHSC columns.

단면형상에 따른 초고강도 콘크리트 기둥의 수화열 특성

초고층 빌딩 건설에 있어서 초고강도 콘크리트는 필수적으로 사용되기 때문에 관련연구 또한 증가하고 있다. 이러한 초고강도 콘크리트 배합에는 다량의 시멘트 결합재가 사용되기 때문에 수화열에 의한 온도균열을 평가하고 제어해야만 현장 적용이 가능하다. 본 연구에서는 초고강도 콘크리트의 단열온도상승시험 결과를 이용한 유한요소해석을 통해 초고강도 콘크리트 기둥의 온도균열 분석을 수행하였다. 초고강도 콘크리트 기둥의 형상을 원형과 사각형으로 모델링하여 기둥 형상에 따른 온도, 응력변화 및 온도균열지수를 분석하였다. 그 결과 원형기둥이 사각기둥에 비해 온도균열저항에 더 효과가 있는 것을 확인할 수 있었다. Study on ultra-high-strength concrete(UHSC) has increased since it is essential in skyscraper construction. Since UHSC mixture has a large amount of the cementitious materials, UHSC can be applied on-site only when its thermal crack behavior due to heat of hydration is evaluated and controlled. In this study, finite element analysis using adiabatic temperature rise test data of UHSC was performed to evaluate thermal crack of UHSC columns. By modeling of circular and square UHSC columns, the characteristics of hydration heat, thermal stress, and thermal crack ratio were investigated according to column shape. As a result, it was confirmed that circular columns are more effective in thermal crack resistance than the square column.

Evaluation of the mechanical properties of 200 MPa ultra-high-strength concrete at elevated temperatures and residual strength of column

In this study, material properties of ultra-high-strength concrete (UHSC) and residual load of reinforced concrete column have been evaluated at elevated temperature. On the basis of the results of experiments, prediction process for residual load of column member subjected to elevated temperature have been proposed. For evaluation on mechanical properties at elevated temperature of UHSC, 100×200mm cylinder specimen of 100, 150, 200MPa was heated to 100, 200, 300, 500 and 700°C by 1°C/min. After that, the ratio of compressive strength at room temperature to compressive strength at elevated temperature was measured. Also, comparison evaluation between experimental results of this paper and previously presented properties of compressive strength properties of normal strength concrete (NSC) and high strength concrete was carried out. Reinforced concrete column member was made of 200MPa concrete and was heated by ISO-834 standard heating curve for 3h. Internal force degradation and fire resistance performance of column member was evaluated by measuring internal temperature and axial deformation. Also, after heating, residual axial load capacity was evaluated through natural cooling for 24h. Prediction process of residual internal force of UHSC column was proposed by deriving model for internal force degradation with experimental results of residual mechanical properties and spalling properties of UHSC subjected to elevated temperature. Based on the experimental results, it was observed that internal force degradation of UHSC by elevated temperature occurred more than that of NSC. In the test for fire resistance performance of column, 26% of section was lost due to spalling, however, it was observed that residual internal force was 52% of design axial load.

The behavior of ultra-high-strength reinforced concrete columns under axial and cyclic lateral loads

In general Ultra High Strength Concrete (UHSC) is a new class of concrete that has been developed in recent decades. UHSC is characterized by extraordinary mechanical and durability properties. The UHSC-Matrix is very brittle material behavior. In this research an experimental program consists of twelve square UHSC columns is being carried out to study the behavior of UHSC columns subjected to constant axial load combined with cyclic lateral loading in order to simulate the case of seismic action. The main parameters of this program were: longitudinal reinforcement ratio, percentage of steel fiber, stirrups ratio, axial load level and concrete compressive strength. In this experimental program each specimen represents a column extending on both sides from the beam-column connection to the location of the point of inflection. Particular attention is paid to the effect of each variable on the strength enhancement, stiffness degradation, energy dissipation capacity, curvature ductility and displacement ductility of the tested columns. Valuable conclusions were obtained from the research results. By increasing the concrete compressive strength the column capacity increases accompanied by a decreasing in the ductility aspects, increasing the longitudinal steel ratio from 2% to (3.6% and 4.5%) leading to an increase in the column capacity and ductility aspect of the tested columns. Using steel fiber between (1.33–2.67)% is recommended in UHSC columns in seismic zones. The Egyptian concrete code of practice limits for the columns stirrups is suitable in seismic zones for columns subjected to a low axial load level.

Effect of Confinement on the Axial Load Response of Ultrahigh-Strength Concrete Columns

AbstractTwelve ultrahigh-strength concrete (UHSC) columns confined by rectangular hoops and crossties were constructed and tested under pure axial load. Primary variables of the investigation were the amount, spacing, and configuration of transverse reinforcement, and concrete compressive strength, ranging from 50 to 200 MPa. The amount of transverse reinforcement ranged from 53 to 151% of that required by the American Concrete Institute (ACI) seismic design provisions. Four different configurations of transverse reinforcement were investigated that included hoops as well as hoops and crossties. The behavior of UHSC columns are characterized by sudden spalling of the concrete cover and extremely brittle failure unless the columns are adequately confined with transverse reinforcement. Therefore, more confinement is required in a column with higher concrete strength than in a column with lower concrete strength to achieve a reasonable postpeak response and sufficient deformability. The amount of transverse ...

Effect of Steel Fibers on the Performance of Ultrahigh-Strength Concrete Columns

This study investigates the effect of the volume fraction of steel fibers on the axial load response of 200 MPa ultrahigh-strength concrete (UHSC) columns. Behavioral aspects investigated include strength, ductility, and delay and control of brittle concrete cover spalling. In addition, the influence of the amount of transverse reinforcement and the combined effect of transverse reinforcement and steel fibers on the postpeak behavior of the 200 MPa UHSC columns were investigated. Two series of columns, having different amounts of transverse reinforcement, ρsh=3.6 and 6.1%, were constructed and tested under pure axial compressive loading. Each series consisted of three columns with three different steel fiber volume fractions (vf=0, 1, and 1.5%). Test results demonstrated that an increase of transverse reinforcement amounts in 200 MPa UHSC columns improves the maximum confined concrete strength and significantly improves the postpeak ductility. The addition of steel fibers resulted in increased peak loads for both the poorly and well confined 200 MPa UHSC columns by delaying and controlling initial cover spalling. The addition of steel fibers improves the confined concrete strength and significantly improves postpeak ductility only for the well confined UHSC columns.

Development of cement-based strain sensor for health monitoring of ultra high strength concrete

In this research a cement-based strain sensor (CBSS) with high strength and self-sensing ability is developed, and the use of the high strength CBSS for structural health monitoring of ultra high strength concrete (UHSC) columns is evaluated. Results show that the CBSS with 0.5% brass-coated steel fibers has high compressive strength of >120MPa. Its piezoresistivity shows little noise, indicating the resistance of the CBSS varies smoothly with the strain. After oven-drying, the repeatability and sensitivity of the piezoresistivity has greatly improved. When the CBSS is embedded in a UHSC column, damage monitoring of the UHSC column can be performed by means of increasing irreversible change in the resistance of the embedded CBSS. The embedded CBSS can sense strain as well as stress of the UHSC column up to a stress of 154MPa. The piezoresistive behavior of the embedded CBSS undergoes three phases during the monotonic loading, and they are high sensitive, linear phase; medium sensitive, nonlinear phase; low sensitive, linear phase with the increase in load.

Eccentric Axial Load Capacity of High-Strength Steel-Concrete Composite Columns of Various Sectional Shapes

AbstractTwo concrete-filled steel tube columns and four concrete-encased steel columns using high-strength steel (yield strength fys=913, 806, and 812 MPa) and high-strength concrete (compressive strength fc′=94, 113, 104, and 184 MPa) were tested to investigate the effect of various sectional shapes and configurations on the eccentric axial load carrying capacity. This study focused on maximizing the contribution of the high-strength steel, preventing early crushing of the concrete (1) by using steel tubes or closely spaced ties for lateral confinement, (2) by using ultra high-strength (200 MPa) concrete with a high-crushing strain, and (3) by placing L-shaped steel sections at the corners of the cross section. The test results showed that the steel tube successfully restrained early concrete crushing and developed its full plastic stress; unlike expectation, early crushing occurred in the ultra high-strength concrete column; and the concrete-encased L-section column had higher peak strength and flexural...

Stress distribution and crack formation in full-scaled ultra-high strength concrete columns

Full-scaled model columns were placed both in summer and winter with an ultra-high strength concrete with a compressive strength more than 150 MPa, and stress distribution and cracking were experimentally evaluated. Specimens placed in summer exhibited cracks around the steel reinforcements which sometimes joined together. Specimens placed in winter showed, in addition to the cracks around the reinforcement, an internal crack perpendicular to the column axis as well as at the specimen surface. These cracks were found to be dependent on the temperature history due to hydration heat liberation and associated autogenous shrinkage strains. It was shown that the autogenous shrinkage of concrete increased when temperature after mixing was low and the maximum temperature during temperature history was high. This accounts for the numerous cracks found in the specimen placed in winter. Strain perpendicular to the axial direction was smaller than that of the axial direction implying the tensile stress due to autogenous shrinkage acting perpendicular to the axial direction as far as the autogenous shrinkage is isotropic. Finite element analysis confirmed the lateral stress due to autogenous shrinkage. Possible influences of autogenous shrinkage of ultra-high strength concrete on the structural performance include (1) early spalling of cover concrete and degradation of flexural strength, (2) degradation of bond and shear strength, and (3) prospect of longitudinal crack in center of the column and degradation of flexural strength.

Crack Resistance of Connections of Cross Shaped Steel Encased Ultra High-Strength Concrete Column to RC Beam under Cycle Loads

In order to investigate the crack resistance capacity of cross shaped steel encased ultra high-strength concrete (CSSEUHSC) column to reinforced concrete (RC) beam connection subjected to reversal cycle load, six interior joint specimens were tested with various axial load ratio nt and volumetric stirrup ratio ρv. A discussion on the crack resistance capacity was presented. Calculation methods of crack resistance capacity were deduced and calculating results were in good agreement with the experimental results. The research results indicated that parameters of CSSEUHSC column to RC beam connection with better crack resistance performance may be referred for engineering application.

Seismic behavior of steel reinforced ultra high strength concrete column and reinforced concrete beam connection

To investigate the seismic behavior of connections composed of steel reinforced ultra high strength concrete (SRUHSC) column and reinforced concrete (RC) beam, six interior strong-column-weak-beam connection specimens were tested subjected to reversal cyclic load. Effects of applied axial load ratio and volumetric stirrup ratio on ductility, energy dissipation capacity, strength degradation and rigidity degradation were discussed. It was found that all connection specimens failed in bending in a ductile manner with a beam plastic hinge. The ductility and energy dissipation capacity increased with the decrease of applied axial load ratio or increase of volumetric stirrup ratio. The displacement ductility coefficient and equivalent damping coefficient lay between those of steel reinforced ordinary concrete connection and those of reinforced concrete connection. The applied axial load ratio and volumetric stirrup ratio had less influence on the strength degradation and more influence on the stiffness degradation. The stiffness degraded sharply with the decrease of volumetric stirrup ratio or increase of applied axial load ratio. The experimental results indicate that SRUHSC column and RC beam connection exhibited better seismic performance and can provide reference for engineering application.

강섬유 보강 초고강도 콘크리트의 확대 타설을 통한 기둥 하중 전달 성능 향상

This study reports on the structural characteristics of slab-column connections using fiber-reinforced ultra-high-strength concrete (UHSC). Compression tests were performed on two slab-column and four isolated column specimens. In the column load tests, slab loads were also applied on the slab-column specimens so that the actual confinement condition at the slab-column joint was considered. The main parameter investigated was the of fiber-reinforced UHSC. This paper also investigates the effects of some parameters, such as confinement of slab concrete, steel fibers, and concrete strength of the joint, related to the ability of the slab-column specimens and isolated column specimens without the surrounding slab to transmit axial loads from the UHSC columns through slab-column connections. Furthermore, the ACI Code (2005) and the CSA Standard (2004) are compared to the experimental results. The beneficial effects of the puddling of fiber-reinforced UHSC on the transmission of column loads through slab-column connections are demonstrated.

100 MPa 초고강도 콘크리트 띠철근 기둥의 이력거동에 관한 실험적 연구

An experimental investigation was conducted to examine the hysteretic behaviors of ultra-high strength concrete tied columns. The purpose of this study is to investigate the safety of ultra-high strength concrete columns with 100 MPa compressive strength for the requirement of ACI provisions. Eight 1/3 scaled columns were fabricated to simulate an 1/2 story of actual structural members with the cross section and the aspect ratio 4. The main variables are axial load ratio, configurations and volumetric ratios of transverse reinforcement. The results show that the deformability of columns are affected by the configurations and volumetric ratios of transverse reinforcement. Especially, it has been found that the behavior of columns are affected by axial load ratio rather than the amounts and the configurations of transverse reinforcement. Consequently, to secure the ductile behavior of 100 MPa ultra-high strength concrete columns, ACI provisions for the requirement of transverse steel may considered axial load level and the details of transverse reinforcement.

Confinement Reinforcement Design Considerations for Ductile HSC Columns

This paper presents results from a continuing research program that aims to study confinement of concrete by lateral reinforcement. The current work deals with the experimental behavior of high-strength concrete (HSC) and ultrahigh-strength concrete (UHSC) column behavior. Realistically sized columns (305 × 305 × 1,473 mm) with heavy stubs (508 × 762 × 813 mm) were tested under moderate to high axial load levels and reversed cyclic displacement excursions. The behavior of UHSC and HSC columns was examined and compared to normal strength concrete column behavior. The variables studied in this research program are the concrete strength, axial load level, steel configuration, amount of lateral steel, and the presence of a heavy stub. A performance-based design procedure for the design of confinement reinforcement in HSC and UHSC columns is presented and compared with current American Concrete Institute (United States) and New Zealand Standards (New Zealand) codes.