Najif Ismail

Cyclic Out-of-Plane Behavior of Slender Clay Brick Masonry Walls Seismically Strengthened Using Posttensioning

AbstractEquations for the design of a posttensioned seismic retrofit of unreinforced clay brick masonry walls are discussed, and results from an associated experimental program are reported. A total of eight full-scale multiwythe vintage solid clay brick masonry walls were subjected to uniformly distributed one-directional and reverse cyclic out-of-plane loading, of which two walls were tested as built and six walls were seismically retrofitted using unbonded posttensioning. Test wall configurations and constituent masonry materials were selected to replicate typical characteristics of historic clay brick masonry walls. The test walls were seismically retrofitted by applying varying magnitudes of posttensioning using a single tendon inserted into a cavity located at the center of each test wall. Several aspects pertaining to the seismic behavior of posttensioned masonry walls were investigated, including damage patterns, force-displacement behavior, tendon stress variation, wall secant stiffness, hysteret...

Performance of Wall to Diaphragm Anchors for Use in Seismic Upgrade of Heritage Masonry Buildings

ABSTRACT Performance of wall to diaphragm (WD) anchors in heritage unreinforced masonry (URM) buildings during the recent New Zealand earthquake series is commented on, detailing typical failure modes. Current building code provisions for the design of masonry anchors are discussed and overview of an associated experimental program investigating the effectiveness of a relatively new type of retrofit WD anchors is presented. A total of 40 anchors were tested for pull out capacity (POC), of which 30 were installed in salvaged heritage material assemblages and 10 were tested in-situ at a heritage URM building. The POC of anchors ranged from 13.01 kN to 23.12 kN when installed in a heritage URM wall and between 9.54 kN and 12.16 kN when driven from side into two consecutive floor joists of a heritage timber diaphragm. Investigated also were the effects of embedment length, installation quality, anchor location, condition of masonry, and condition of substrate materials on anchor performance.

Building Typologies Prevalent in Northern Pakistan and Their Performance during the 2015 Hindu Kush Earthquake

The M7.5 earthquake of 26 October 2015 resulted due to reverse faulting at an intermediate depth of 210 km within the northeast-trending tabular zone underneath the Hindu Kush region, with its epicenter located 45 km southwest of Jarm in Afghanistan. In Pakistan alone, the earthquake and subsequent aftershock swarm resulted in 280 fatalities, injuries to 1,770 persons, and notable damage to 109,123 buildings. A synopsis of observations is presented herein, covering details about seismotectonics, strong motion characteristics, damage statistics, and typical building failure modes. Building damage was observed to mostly concentrate in vulnerable rural and old unreinforced masonry buildings, with aspects such as complete or partial out of plane collapse of walls, collapse of roofs due to loss of seating, shear cracking in masonry walls/panels, shear and flexural damage in masonry spandrels, cracking at infill-frame interface, damage at building corners, pounding damage, toppled minarets, and damage due to ground settlement.

Effect of process parameters on the performance of fly ash/GGBS blended geopolymer composites

Alkali activation of fly ash and ground-granulated blast-furnace slag (GGBS) is a sustainable technology that promotes recycling of industrial by-products in the form of geopolymer composites. In this study, geopolymers are prepared with fly ash, GGBS, and desert dune sand (fines). The alkaline activator solution is formulated using sodium silicate and 14 M sodium hydroxide solutions. The effect of mixture proportioning and curing conditions on the workability, setting time, and compressive strength of geopolymers was examined. The investigated process parameters included percentage of fly ash replacement by GGBS, superplasticizer dosage, amount of fines, alkaline activator solution content, and sodium silicate to sodium hydroxide ratio. The final geopolymeric product could be enhanced by employing subsequent continuous and intermittent water curing techniques. Based on the experimental results, analytical models correlating mixture proportions with workability and 28-day compressive strength were developed for geopolymers made with 100% GGBS and equal proportions of fly ash and GGBS.