A new type of composite column is presented and assessed through experimental testing and numerical modeling. The objective of this research is to investigate design options for a composite column without the use of ferrous materials. This is to avoid the current problem of deterioration of concrete due to expansion of rusting reinforcement members. Such a target can be achieved by replacing the steel reinforcement of concrete columns with pultruded I-shape glass FRP structural sections. The composite column utilizes a glass FRP tube that surrounds a pultruded I-section glass FRP, which is subsequently filled with concrete. The GFRP tube acts as a stay-in-place form in addition to providing confinement to the concrete. A total of four composite columns were tested under monotonic axial loading. The experimental ultimate capacity of each of the tested composite column was compared to the predicted numerical capacity using ANSYS program. The comparison showed that the predicted numerical values were in good agreement with the experimental ones.

The most common method of strengthening columns with FRP is confining their external environment. Confining is effective for compression members and use for increase load carrying capacity or for increase ductility. The main target in this research is investigation strengthening of RC columns with multi directional FRP composites. For this purpose first, 3 available experimental specimens were modeled in ABAQUS software. So, accuracy of this modeling proved, by Comparison and proximity the result of experimental and software. Then 18 analytical specimens were modeled with considering variables such fiber gender, direction of composites layers and percent of longitudinal steel of column section, in ABAQUS software. Analytical specimen divided to the two groups, half of them with 2 percent longitudinal steel and the other half with 4 percent steel. In every group were considered a specimen without strengthening, four specimens confined with CFRP sheets and four specimens confined with GFRP sheets. Beside specimens of every group strengthened with composite layers in different directions 0, 0, 0 degrees and 90, 0, 90 degrees and -45, 45, 0 degrees and -45, 45, 90 degrees. The finite elements analysis results of these specimens shows that multi directional FRP composites increases 1.34 to 2.77 times the axial load carrying capacity of strengthened columns and 5.5 to 13 time their ductility. Strengthening by FRP composites with layers in direction of -45, 45, 0 degree, is good method for increasing the ductility of columns. Also effect of strengthening the specimens with two percent steel section are 8 to 16 percent more than specimens with four percent steel section.

هدف از این تحقیق، تولید کامپوزیت زمینه آلیاژهای مس تقویت شده با ذرات الماس میکرونی و بررسی خواص مکانیکی این کامپوزیت است. از مهم ترین مسائل ساخت این نوع کامپوزیت ، بهینه سازی استحکام ذرات الماس در زمینه فلزی و خواص سایشی مد نظر این نوع کامپوزیت است. پودرهای کامپوزیتی با استفاده از آسیابکاری پرانرژی (سایشی) و به روش سینتر پرس داغ تولید شدند. به منظور بررسی استحکام خمشی، سختی و خواص سایشی، نمونه ها با اضافه کردن فلزات مختلف به زمینه، شرایط مختلف آسیابکاری و پارامترهای مختلف فشار داغ، ساخته شدند. هدف از این تحقیق، تولید کامپوزیت زمینه آلیاژهای مس تقویت شده با ذرات الماس میکرونی و بررسی خواص مکانیکی این کامپوزیت است. از مهم ترین مسائل ساخت این نوع کامپوزیت ، بهینه سازی استحکام ذرات الماس در زمینه فلزی و خواص سایشی مد نظر این نوع کامپوزیت است. پودرهای کامپوزیتی با استفاده از آسیابکاری پرانرژی (سایشی) و به روش سینتر پرس داغ تولید شدند. به منظور بررسی استحکام خمشی، سختی و خواص سایشی، نمونه ها با اضافه کردن فلزات مختلف به زمینه، شرایط مختلف آسیابکاری و پارامترهای مختلف فشار داغ، ساخته شدند.

Structural damage detection is one of the primary goals of structural health monitoring. Minimum safety can be provided upon timely identification of the damaged elements and appropriate decisions (repairing or replacing the damaged elements). Today, the use of concrete-filled steel tube composite columns in the construction industry, especially high-rise buildings, is increasing. In these columns, the concrete core debonding from the steel tube is considered a prevalent type of damage. This study discusses the impact of such debonding on dynamic modal properties (natural frequencies and vibration mode shapes) and the detection of debonding damage area based on wavelet analysis. Debonding to a depth of 3 mm is defined as reduction of concrete stiffness in connection with the steel tube, and the column was subjected to frequency analysis. Modal information, including frequency values and vibration mode shapes, were extracted. Differences in frequency values and Modal Assurance Criterion (MAC) smaller than one were observed between primary and secondary shapes of vibrational modes due to the presence of debonded areas. The results showed that with the addition of a new debonding damaged area, the rate of reduction of frequency values increased. The damage index was proposed based on the detail coefficients obtained from discrete wavelet analysis of primary and secondary shapes of vibration modes to identify the area of detachment damage. The results demonstrated that the relative minimum and maximum values of the damage index for all modes occurred in debonding damaged areas. Moreover, the damage index values for different damaged areas were independent of each other. Indeed, the damage index values for other debonding damage situations did not change when a new debonding damaged area was added. This is a positive point in the damage detection process with multiple debonded areas because in this case, the inability to detect a debonding damaged area cannot affect the detection of other debonding damage situations.

In this research the hollow steel columns that strengthened with CFRPunder axial compression has been investigated. Retrofit methods such as the use of steel plates increases the structural weight and in some cases using such method is difficult and impossible. This paper reports experimental and numerical modeling using ANSYS software. To determine the ultimate load of square hollow section (SHS) steel columns, seven samples of SHS steel columns with dimensions of 90 × 90 × 2.5 mm which were strengthened with CFRP and two control samples were tested. The results of numerical model was validated with experimental results. The results showed that, when the coverage of CFRP layers is not complete, CFRP has no effect on increase of the compressive axial load of SHS steel columns. In addition, the results showed that, the number, direction, and the coverage of CFRP layers can be effectively increase the pressure capacity of SHS steel columns.

Carbon nano-materials, especially Carbon nanotubes (CNTs(, are the most prospective advanced materials for application in cement-based products for the construction industry due to their excellent material properties. An appropriate design for beam-column joint structures is required to meet the requirements of strength and ductility to prevent any sudden failure. Under seismic action, this beam-column joint zone is considered the most sensitive zone that undergoes different shear stresses in different deflections. The seismic performance of beam-column connections and joints can be enhanced by using improved details in the joints, ensuring a strong connection behavior. However, the use of dense reinforcements brings about executive problems such as lack of concrete condensation. This paper investigates the effect of Engineering Cementitious Composites containing Carbon Nanotubes (ECC-CNT) on the behavior of RC exterior beam-column joints under reversed cyclic loading. In this study, three beam-column concrete joints were tested, one of which was the reference specimen. The two other joints of the critical area of beam-column connection were replaced with Engineering Cementitious Composite (ECC) and ECC-CNT. The main parameters considered include the moment-deflection relationship, the energy absorption capacity, hysteresis curve, and crack propagation. The specimen was subjected to a reversed cyclic loading under control deformation at the tip of the beam. Loading continued until the load dropped to more than 30-40% of the maximum load. Also, to simulate the actual sample, the compressive load of fifteen tons continuously entered the column. The mixing technique for producing highly dispersed nanomaterial in cement mortar is crucial as it directly affects the mechanical properties of the cementitious composite. In this study, a surfactant (plasticizer) and Arabic Gum were used in order to get a homogenous dispersion of CNT in water. According to the results in the sample containing CNT in the plastic joint, it absorbs the highest amount of energy at the end of loading, which was 28% and 55% higher than ECC and NC, respectively. In addition, results indicated that the use of ECC-CNT in the plastic bonding zone had a significant effect on the energy absorption and relative deformation of the joints.