Engineered Cementitious Composites Effects on Seismic Strengthening of Non-ductile RC frames with masonry infills

Performance of fiber reinforced Engineered Cementitious Composites (ECC) strengthened by non-ductile Reinforced Concrete (RC) frames with hollow clay brick masonry infill subjected to quasi-static in-plane loading was experimentally assessed herein. The suggested strengthening technique was used for increasing the lateral strength of infilled RC frames and retaining the integrity of the masonry infill wall during earthquake loading. Initially, the mechanical properties of ECC and masonry elements were tested. The ECC was made of water, cement, silica fume (5% of cement weight), Zeolit (5% of cement weight), silica sand, fly ash, superplasticizer, and Poly-Vinil-Alkaol fibers (1.5% of the whole volume of the concrete). Cylinder and Dog-bone specimens were cast and tested to evaluate the compressive and tensile stress-strain behavior of ECC concrete. Afterward, three RC specimens with one-third scale and one bay-single story. Of these specimens, one frame was tested as built without infill (BF) and another frame as built with infill (IF-E0), and the rest of the frames were retrofitted using ECC as an overlay on the masonry wall (IF-DF-E20-1). The infilled frame strengthening using ECC (IF-DF-E20-1) provided lateral strength, stiffness, and energy dissipation capacity of 2.31, 1.11, 1.37 times those of the hollow clay brick masonry infilled frame (IF-E0), respectively. Furthermore, the obtained backbone curves are idealized using a two-line model. The relative displacement of each floor is an important issue in the structural and non-structural seismic designs; thus, the initial cracks (flexural in columns, diagonal in beam-column joint, flexural in beams, cracking in the interface of the frame and infilled bricks, crushing of bricks, shear crack in column, sudden crushing of infill, and concrete crushing of column) at the respected displacement was analyzed here. According to the results, the proposed strengthening technique not only increased the lateral strength and energy absorption capacity of the infilled frame but also provided a reasonable system overstrength and prevented brittle failure modes in the infill wall

E‌X‌P‌E‌R‌I‌M‌E‌N‌T‌A‌L I‌N‌V‌E‌S‌T‌I‌G‌A‌T‌I‌O‌N T‌H‌E M‌E‌C‌H‌A‌N‌I‌C‌A‌L A‌N‌D S‌T‌R‌U‌C‌T‌U‌R‌A‌L S‌T‌R‌E‌N‌G‌T‌H‌S O‌F C‌O‌N‌C‌R‌E‌T‌E‌S C‌O‌M‌B‌I‌N‌E‌D R‌U‌B‌B‌E‌R W‌A‌S‌T‌E‌S A‌N‌D F‌I‌B‌E‌R‌S

The current research deals with the use of waste rubber powder with different forms and percentages as a replacement for the fine aggregates in concrete production for the purpose of examining different mechanical and structural properties at an experimental level. The mixed design of common concrete as well as other mixed designs having waste rubber powder were constructed. The amounts of waste rubber were equivalent to 5, 10, and 15% of actual volume of the aggregate. To remove the negative effects on some mechanical properties of the product such as compressive and tensile strength and impact resistance, the synthetic Polyphenylene Sulfide (PPS) fibers known as synthetic complex fibers with 0.75 and 1.5% were added to the concrete having waste rubber powder. The first part of this research examines the effects of the combination of fibers with waste rubber powder on the compressive, tensile, flexural strength, and impact resistance of specimens. Also, in the second part of this research, six concrete slabs were constructed with the structural performance of such concrete in road construction under elastic basement under direct loading. The displacement-load curve of the samples as well as the failure pattern of the samples were observed and analyzed. The result of the experiments on the standard specimen in the first part of this research showed that despite the decrease in compressive strength due to the simultaneous addition of rubber powder compared to the common concrete samples, the tensile, flexural strength, and impact resistance were improved compared to the samples constructed with common concrete. By replacing 15% rubber powder instead of the fine aggregates, the final impact resistance increased up to 48%. Simultaneous addition of 0.75 % fibers and 5% rubber doubled the impact resistance of the concrete. It is worth mentioning that 1.5% addition of fibers to the concrete having 5% rubber power increased final impact resistance up to 5.72 times of that of Ref concrete. The results of the second part of this research showed that the final capacity of fiber-rubber concrete slabs under elastic basement to have favorite flexural behavior as concrete pavement compared to common concrete slab increased up to 50%; meanwhile, the amount of absorbed energy and the strength of combined concrete slabs of rubber wastes and fibers were 3 times higher than those made by common concrete in the reference sample

Seismic Response of Base-Isolated Structures with LRB and FPS under near Fault Ground Motions

AbstractSeismic response of structures in the vicinity of causative earthquake faults can be significantly different than those observed further away from the seismic source. In the near fault zone, ground motions are significantly influenced by the rupture mechanism and slip direction relative to the site and by the permanent ground displacement at the site resulting from tectonic movement. Forward directivity and fling effects have been identified by the seismologists as the primary characteristics of near fault ground motions. Because of the unique characteristics of the near-fault ground motions and their potential to cause severe damage to structures designed to comply with the criteria mostly based on far-field earthquakes, the estimation of seismic response of base-isolated structures for a project site close to an active fault should account for these special aspects of near fault ground motions. This paper investigates the seismic response of base-isolated structures with LRB and FPS isolators under near fault ground motions. A seismic evaluation of the building, isolated with the LRB and FPS, is performed using a nonlinear three-dimensional analytical model. The parametric study is concentrated on base shear, accelerations and displacements of isolated models. Large displacement and velocity pulses in records of near fault ground motions can significantly change the results of seismic response of base-isolated structures