Sharon, MA, United States
Sharon, MA, United States

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Malhotra P.K.,StrongMotions Inc.
Practice Periodical on Structural Design and Construction | Year: 2017

Seismic shutoff devices are expected to automatically stop the flow of hazardous gases and liquids through distribution systems that may be damaged by earthquakes. There is some uncertainty in the actuation of these devices; they may actuate when not needed and they may not actuate when needed. Therefore, these devices can only reduce, and not eliminate, the risk of hazardous leaks. It is shown in this paper that shutoff devices can be deployed to meet specific performance goals in seismic design. A cost-benefit analysis is conducted to show that devices are most effective in reducing the risk to weak systems in highly seismic areas. The uncertainty in actuation diminishes the effectiveness of these devices. © 2016 American Society of Civil Engineers.


Malhotra P.K.,StrongMotions Inc.
Journal of Structural Engineering | Year: 2011

In the conventional seismic analysis of a system, the input motion is defined either by a probabilistic response spectrum or by ground-motion histories whose spectra match the probabilistic response spectrum. In both cases, it is implicitly assumed that the spectral values at different periods on a probabilistic response spectrum are fully correlated with one another. A nonlinear system changes its effective period during seismic shaking; hence, its response depends on spectral values at many natural periods. The assumption of complete correlation between spectral values at different periods results in an overestimation of the response of a nonlinear system. For the case analyzed in this paper, the conventional use of a 500-year mean return period (MRP) response spectrum in nonlinear analysis produces responses that have 20-30% longer MRPs. Also, the larger-component response acceleration was 11% higher than the geometric-mean response acceleration, and the larger component response deformation was 33% higher than the geometric-mean response deformation. This paper presents a more accurate way of using the response spectrum in the probabilistic analysis of nonlinear systems. © 2011 American Society of Civil Engineers.


Malhotra P.K.,StrongMotions Inc.
Structural Engineering International: Journal of the International Association for Bridge and Structural Engineering (IABSE) | Year: 2012

Natural hazards pose risk to individuals as well as to the society. People are harmed by the damage to structures they own or occupy. People are also harmed by the damage to other structures around them-schools, hospitals, shops, utilities, bridges, etc. As the purpose of engineering design is to reduce the risk, the design standards should attempt to reduce both individual and societal risks from natural hazards. The current design standards attempt only to reduce the risk to individual structures. They are not very effective in reducing the societal (aggregate) risk as will be shown in this paper. Hurricanes in the coastal US are used to illustrate the main point. A new approach is proposed to reduce the societal risk from natural hazards.


Malhotra P.K.,StrongMotions Inc
Structural Engineering International: Journal of the International Association for Bridge and Structural Engineering (IABSE) | Year: 2014

A key lesson from the 2011 Fukushima nuclear disaster has been largely ignored. The Fukushima disaster highlighted the consequence of aggregating (accumulating) risk. With six reactors within a 3,5 km2 site, the Fukushima Daiichi Nuclear Power Plant (NPP) was one of the extreme examples of aggregating risk in a small area. As a result of the 2011 T o hoku earthquake and the following tsunami, core damage (nuclear meltdown) occurred at all three operating reactors at the facility. A multi-reactor facility poses more risk to human health and the environment than a single-reactor facility. Risk aggregation increases the need for mitigation and insurance. But these factors are ignored in the design of NPPs and other facilities. A larger facility places a greater burden of the risk on the government (taxpayers). Whenever possible, the risk should be distributed rather than concentrated. The risk that remains after mitigation is known as the residual risk. There is a cost associated with the residual risk. Whether this cost is borne by the owner or the taxpayers, it should be a factor in the design of a facility. Currently, there are no disincentives to the aggregation of risk in small areas.


Malhotra P.K.,StrongMotions Inc | Nimse P.,Wood Group Kenny | Meekins M.,ITER Organization
Structural Engineering International: Journal of the International Association for Bridge and Structural Engineering (IABSE) | Year: 2014

A horizontal water storage tank was analyzed for seismic shaking at the ITER Tokamak Complex in France. The objectives were to (a) estimate the seismic forces in the tank; (b) calculate the sloshing response of the tank; (c) determine if baffles are needed to control sloshing; and (d) evaluate the possibility of using a single fixed support in the longitudinal direction to allow free thermal expansion of the tank. An approximate conservative analysis predicted very high sloshing waves and seismic forces in the tank. The fluid-structure interaction in the tank showed that only about 28% of the liquid moves with the tank wall and generates seismic forces in the longitudinal direction. The remaining 72% of the liquid sloshes near the free surface and does not generate significant seismic forces. The sloshing wave is not high enough in the longitudinal direction as the fundamental sloshing mode is not excited because of its very low natural frequency. Hence, baffles are not needed to control sloshing. The seismic force is low enough for a single fixed support to resist the entire seismic force in the longitudinal direction.


Malhotra P.K.,StrongMotions Inc.
Structural Engineering International: Journal of the International Association for Bridge and Structural Engineering (IABSE) | Year: 2014

The design requirements for electric power transmission lines in the USA address only the risk of injury and death from construction, operation, and maintenance. They do not explicitly address the risk to operators (owners) and consumers from the disruption of power supply. Like most structures, transmission lines are designed for wind speeds with "low" probability of exceedance at specific locations. Unlike most structures, transmission lines can be damaged by winds anywhere along their length. As a result, the probability of disruption to a transmission line can be significantly greater than the probability of exceeding the design wind speed at any specific location. In this paper, it is shown that a 1076 km (669 mi) long transmission line designed for 700-year mean return period (MRP) wind speeds is damaged with an MRP of only 54 years. Hence, the design based on site-specific criterion provides a low perception of the risk to a transmission line. A risk-based approach is proposed to evaluate and select the design criterion for transmission lines. It is more economical in the long run to design a longer transmission line to a higher criterion than a shorter transmission line.


Malhotra P.K.,StrongMotions Inc.
Structural Engineering International: Journal of the International Association for Bridge and Structural Engineering (IABSE) | Year: 2013

Long continuous structures such as pipelines, power transmission lines, and high-speed rails are exposed to hazards throughout their length. These hazards should be accumulated (aggregated) along the entire length of these structures to (a) assess the risk and (b) establish design criteria for reducing the risk to a tolerable level. The design loads for structures are usually derived from site- specific probabilistic hazard analyses. It is shown in this paper that the site-specific hazard analysis underestimates the risk to long continuous structures. Aggregate hazard analysis is proposed to select the design criteria for these structures. The data used in this study are for earthquake ground motions in California, but the conclusions should be applicable to all hazards along long continuous structures anywhere in the world.

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