Ground Motion Characteristics of the 2015 Gorkha Earthquake, Survey of Damage to Stone Masonry Structures and Structural Field Tests

Abstract

On April 25, 2015, a M7.8 earthquake rattled central Nepal; ground motion recorded in Kantipath, Kathmandu, 76.86 km east of the epicenter suggested that the low-frequency component was dominant. We consider data from eight aftershocks following the Gorkha earthquake and analyze ground motion characteristics; we found that most of the ground motion records are dominated by low frequencies for events with a moment magnitude >6. The Gorkha earthquake devastated hundreds of thousands of structures. In the countryside, and especially in rural mountainous areas, most of the buildings that collapsed were stone masonry constructions. Detailed damage assessments of stone masonry buildings in Harmi Gorkha was done, with an epicentral distance of about 17 km. Structures were categorized as large, medium, and small depending on their plinth area size and number of stories. Most of the structures in the area were damaged; interestingly, all ridge-line structures were heavily damaged. Moreover, Schmidt hammer tests were undertaken to determine the compressive strength of stone masonry and brick masonry with mud mortar for normal buildings and historical monuments. The compressive strengths of stone masonry and brick masonry were found to be 12.38 and 18.75 MPa, respectively. Historical structures constructed with special bricks had a compressive strength of 29.50 MPa. Pullout tests were also conducted to determine the stone masonry-mud mortar bond strength. The cohesive strength of mud mortar and the coefficient of friction were determined.

Strong-Motion Characteristics and Visual Damage Assessment Around Seismic Stations in Kathmandu after the 2015 Gorkha, Nepal, Earthquake

“…We can see that this intensity is high for TVU (I*, Table 3) during the Gorkha Earthquake. It is worth noting that the response of TVU (Figure 11) is higher than those of other sites not only in 1-2 s range but in broad range of 0.5-3 s. The damage of buildings may not be related to the predominant period of the building alone as most of the low rise and medium rise buildings in the Kathmandu Valley have a predominant period of 0.1-0.2 s (Parajuli and Kiyono 2015) but the response of TVU in the 0.1-0.2 s range is not the highest. The site TVU suffered the heaviest damage among the four stations and the parameter I* can directly be associated with the building damage.…”

The influence of interface geometry, stiffness, and crushing on the dynamic response of masonry collapse mechanisms

“…To illustrate different possible applications of the model, 2 different sets of joint stiffnesses and a range of compressive strengths were considered in the analysis. The compressive strengths were chosen based on the range of values provided in the Italian Building Code for brick masonry with lime mortar, as well as the results of both in‐situ and experimental tests conducted on brick masonry structures in Nepal . Similarly, the first set of joint stiffnesses—varying from flexible ( k n = 85 MPa/m) to very stiff ( k n = 13.5 GPa/m)—were chosen with the objective of exemplifying how foundation stiffness could be taken into account in the model, and were selected based on similar analyses conducted in Lipo and Felice, Lipo and Felice, and Al Shawa .…”

“…The compressive strengths were chosen based on the range of values provided in the Italian Building Code for brick masonry with lime mortar, 19 as well as the results of both in-situ and experimental tests conducted on brick masonry structures in Nepal. 20,21 Similarly, the first set of joint stiffnesses-varying from flexible (k n = 85 MPa/m) to very stiff (k n = 13.5 GPa/m)-were chosen with the objective of exemplifying how foundation stiffness could be taken into account in the model, and were selected based on similar analyses conducted in Lipo and Felice, 10 Lipo and Felice, 11 and Al Shawa. 13 The second set of stiffnesses is representative of interfaces within the structure-modelling both the stiffness of a single interface (k n = 200, 500, 1500 GPa/m) as well as the deformation associated with a larger portion of the structure in the vicinity of the interface (k n = 2, 5, 15 GPa/m), with the latter having been found to lead to an overall reduction in dynamic capacity.…”

Conservation of Cultural Heritage: Issues along the Thapathali-Teku stretch of the Bagmati River in Kathmandu, Nepal

“…Almost all of the sattals are rented out to generate income; few were sold out, and a lack of periodic maintenance and repair of these structures left them gradually dilapidated. The massive earthquake in April 2015 acted as the catalyst to transfigure these structures which are more vulnerable and risk leading to decay and collapse [5][6][7][8]. Many are in a ruined condition and still inhabited; few have collapsed, waiting for the restoration and reconstruction, few are reconstructed in reinforced cement concrete.…”