5 research outputs found
Gravity Load Collapse Behavior of Nonengineered Reinforced Concrete Columns
Get PDFThis paper aims at investigating gravity load collapse behavior of extremely poor quality reinforced concrete columns under cyclic loading. Such columns were usually constructed by local people and may not be designed to meet any of the standards. It was found that their concrete strength may be as low as 5 MPa and the amount of longitudinal reinforcement may be lower than 1%. This type of column is deliberately defined as “nonengineered reinforced concrete column,” or NRCC. During earthquake, the gravity load collapse of the NRCC columns caused a large number of death tolls around the world. In this study, four columns as representative of existing NRCC were tested under cyclic loading. The compressive strength of concrete in order of 5 MPa was used to be representative of columns with poor quality concrete. Two axial load levels of 6 and 18 tons were used to study the influence of axial load level on maximum drift at gravity load collapse. To investigate the effect of bar types on drift capacity, 9 mm round bars were used in two specimens and 12 mm deformed bars were used for the rest of the specimens. The maximum drift before gravity load collapse was very dependent on the axial load level. The maximum drift of the specimens subjected to high axial load (18 tons) was extremely low at approximately 1.75% drifts. The use of deformed bars (associated with larger amount of longitudinal reinforcement) caused the damage to severely dissipate all over the height of the columns. Such damage caused columns to collapse at a lower drift compared to those using round bars. Finally, the plastic hinge model was used to predict the maximum drift of the low strength columns. It was found that the model overly underestimates the drift at gravity load collapse
Collapse Behavior of Low Strength Concrete under Cyclic Loading
No full textThe paper aims at investigating the failure mechanism of extremely poor quality reinforced concrete (RC) columns with very low amount of longitudinal reinforcement ratio recommended by design standard. This type of column was generally found in many developing country. Four column specimens representative of poor quality columns with similar axial stress but different longitudinal reinforcement ratios and concrete strength were test under cyclic loading. The test result revealed that the lateral drift of the column with higher strength is larger compared to those with lower strength. The amount of longitudinal reinforcement ratio did not significantly affect the maximum drift at collapse but may affect axial shortening at the stage near collapse. It was evidently observed that the axial shortening of the column at the nearly collapse stage of column with higher longitudinal reinforcement ratio is lower than those with lower ratio.</jats:p
Machine Learning and Regression Models for Evaluating Ultimate Performance of Cotton Rope-Confined Recycled Aggregate Concrete
No full textThis study investigates the use of cotton ropes (CRs) as a sustainable and cost-effective substitute for synthetic fiber-reinforced polymers for concrete confinement, offering significant environmental benefits such as lower CO2 emissions and reduced energy consumption. The work evaluates the effectiveness of CR strips for confining concrete, including scenarios with recycled concrete aggregates (ReCA). Compressive strength improvements varied among specimens, with Specimen I-3F showing a 140.52% increase and Specimen II-3F achieving a 46.67% improvement. Strip configurations for Type I recycled aggregate concrete (RAC) outperformed full wraps on Type II RAC, exemplified by Specimen I-3S’s 84.51% improvement. Ultimate strain enhancements ranged from 915% to 4490.91%, driven by the significant rupture strain of cotton rope confinement. For Type I RAC, complete wrapping significantly outperformed strip configurations by 56%, 50%, and 32% in ultimate strength improvement for 1, 2, and 3 layers, respectively. The confinement ratio, varying from 0.10 to 0.70, greatly influenced the compressive behavior, with compressive strength normalized by unconfined strength increasing consistently with the confinement ratio. A minimum confinement ratio of roughly 0.40 is required to achieve an increasing second part in the compressive behavior. The initial parabolic branch was modeled using Popovics’ formulation, revealing an elastic modulus approximately 20% lower than ACI 318-19 predictions. The second branch was described using a linear approximation, and nonlinear regression analysis produced expressions for key points on the idealized compressive curve, enhancing model accuracy for CR-confined RAC. The R2 values for the nonlinear regression analysis performed on experimental results were greater than 0.90. This study highlights the effectiveness of neural network expressions to predict the compressive strength of CR-confined concrete. A strength reduction (ratio of full wrap and strip wrap height CRs) factor of 0.67 was proposed and used for strip-wrapped specimens. It was seen that the neural network models also predicted the compressive strength of partially wrapped specimens with reasonable accuracy using the strength reduction factor
The Performance of Carbon Fiber in Decreasing the Strain Level of the PC-Longitudinal Bridge (PC-Plank Girder) under Service Load
Get PDFงานวิจัยนี้มุ่งเน้นที่จะศึกษาประสิทธิภาพของเส้นใยคาร์บอนไฟเบอร์ในการเพิ่มความแข็งแรงของโครงสร้างแผ่นพื้นของสะพานข้ามคลองแพรกลึก จ.สมุทรสงคราม เนื่องจากสะพานมีการใช้งานมาอย่างยาวนาน จึงได้ทำการตรวจสอบและประเมินกำลังรับน้ำหนักบรรทุกของสะพาน ด้วยการทดสอบกำลังรับน้ำหนักบรรทุกเสมือนจริง ผลของการประเมินความความแข็งแรงของโครงสร้างสะพานได้ถูกนำมาใช้ในการออกแบบการเสริมกำลังโครงสร้างโดยใช้เส้นใยคาร์บอนเสริมโพลิเมอร์(Carbon Fiber Reinforced Polymers: CFRP) จากผลของการเสริมกำลังโครงสร้างโดยการติดตั้งแผ่น CFRP จำนวน 2 ชั้น พบว่า การเสริมกำลังสามารถทำให้ระดับค่าความเครียดและการแอ่นตัวบริเวณกึ่งกลางแผ่นพื้นใต้สะพานโดยรวมมีค่าลดลงร้อยละ 4.33 สำหรับความเครียด และ3.68 สำหรับการแอ่นตัว ซึ่งแสดงให้เห็นว่าการเสริมกำลังด้วย CFRP สามารถช่วยในการลดระดับความเครียด และการแอ่นตัวที่เกิดจากน้ำหนักบรรทุกได้ และจากการประเมินค่าโมเมนต์ดัดในโครงสร้างสะพานส่วนบนโดยวิธี LRFR ค่า Rating Factor (RF) ทั้งระดับ Inventory และระดับ Operation พบว่าหลังเสริมกำลังด้วย CFRP สะพานสามารถรับน้ำหนักบรรทุกเพิ่มขึ้นคิดเป็นร้อยละ 35 แสดงว่า สะพานยังคงสามารถรับน้ำหนักบรรทุกได้เพิ่มขึ้น โดยไม่เกิดการวิบัติและสามารถใช้สะพานได้อย่างปลอดภัยThis research focuses on studying the effectiveness of carbon fiber reinforcement in increasing the strength of the floor structure of the bridge over the Canal Phrae Kluang, Samut Songkhram Province. Due to the prolonged use of the bridge, an inspection and evaluation of the load-bearing capacity of the bridge were conducted through quasi-static load tests. The results of the structural strength assessment were used in the design of structural reinforcement using Carbon Fiber Reinforced Polymers (CFRP). From the results of the reinforcement with the installation of two layers of CFRP, it was found that the reinforcement could reduce the levels of stress and deformation in the middle area of the bridge floor by 4.33% for stress and 3.68% for deformation. This demonstrates that CFRP reinforcement can help in reducing the levels of stress and deformation caused by increased load, and from the assessment of the moment capacity in the upper bridge structure using the LRFR method, both at the Inventory and Operation levels, it was found that after reinforcement with CFRP, the bridge can withstand an increased load capacity by 35%. This indicates that the bridge can still handle an increased load without experiencing failure and can be used safely
Finite Element Investigation of Angle Ring Confinement for Clustered Large-size Stud Shear Connector in Full-Depth Precast Concrete Bridge Deck Panel
Get PDFFull-Depth Precast Concrete (FDPC) bridge deck panel system, consisting of concrete deck and steel girders, has been used widely for highway and bridge construction due to rapid construction and replacement as well as in terms of economics. This system could integrate with clusters of large size headed-stud shear connectors for more significant connection, although larger composite actions were experienced. Therefore, a new angle steel ring confinement was introduced and tested by push-off samples for the most effective shear transfer. The Finite Element Analysis (FEA) of the push-off model with an in-depth investigation of non-linear concrete properties, boundary parameters, and different geometries of angle ring confinement was developed in this study. The FE models were verified with the push-off test in terms of loads, displacements, and failure stages. Nonlinear concrete material models: Concrete Damage (CD) and Drucker Prager (DP) were identified the different abilities either for predicting initial cracks, or determining maximum resistance and critical failure, respectively. The thickness of the angle and the sizes of hook bars were investigated for the most effective aspects of the angle ring confinement. The results showed comparable stiffness and load resistance for various aspects. However, compatible geometries, either 5 mm thick angles with DB12 hook bars or 10 mm angles with DB25 hook bars, were suggested. The final non-linear FEA model was reliable for comparative studies to FDPC push-off with different confinement configurations
