Sustainability Indicators

It is necessary to choose suitable indicators to objectively evaluate LCM scenarios and make decisions.The author proposes to use sustainability indicators for this purpose.Sustainability is defined as a concept based on the environmental,economic and social aspects,and is one of the key issues in a construction sector to be well considered in the 21st century[5].

It is easy to understand that collapse of structure impairs the sustainability because the treatment of debris produced by destruction of structures needs huge energy and reconstruction of structures requires an additional amount of resources and energy.Many people might be killed or injured,and employment and production bases would be temporally unavailable.Engineers keep it in mind what might happens by phenomena that are not covered by the design.Thus,the safety margin or safety redundancy that represents the resistance of structure directly links the social sustainability.As the environmental aspect of sustainability,appropriate indicators are set for environmental impacts in the execution and use stages of the structure,such as resource consumption,greenhouse gas emission,and impacts on the ambient environment.As the economic aspect,all the direct and indirect costs during execution and the use and at the end of life of the structure,as well as the benefits and values provided by the structure,can be set as indicators[6].

It is not so easy to find the best solution among alternatives because no comprehensive indicator exists.For example,when the margin of safety(safety redundancy)is taken more,more resources and energy may be needed for construction and higher construction cost will be consequences,as indicated in Figure 3[7].This is the collision among the sustainability indicators.Therefore,the sufficient balance among each sustainability indicator should be achieved.

Figure 3　Balance between social(safety redundancy),environmental(CO2 emission)and economic(cost)indicators[7]

Sustainability indicators should be well considered in the life-cycle of structure.Durability is directly related to structural performance such as safety and serviceability,while resilience and robustness are related to the safety margin and the mechanism of failure.Sustainability is systemized at each stage of life-cycle to consider in a comprehensive manner,safety and serviceability under the social aspect,cost under the economic aspect,and resources and energy under the environmental aspect.LCM allows for designers to find a good balance between social,economic and environmental indicators.