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Energy Saving in Bridge Engineering Hongjiang LI1 Yanling LENG1 and Ying MA2 1 Research Institute of Highway the Ministry of Communications China P O Box 100088 Beijing PH 086 010 62079558 FAX 086 010 62079556 email hj li 2 College of Transportation Southeast University China P O Box 210096 Nanjing PH 086 025 83794206 email mygw2006 ABSTRACT As energy conservation becomes a significant concern of national socio economic development energy saving for bridge structure is attracting more and more attentions For the purpose of revealing energy problems and exploring energy saving potential in bridge engineering technical condition factors of bridge are analyzed based on the basic concept of energy which have an influence on vehicle fuel consumption and energy problems rooted in materials consumption in bridge construction furthermore energy saving measures are put forward in various aspects in bridge engineering such as planning design construction and maintenance The study shows that most energy problems in bridge engineering belong to indirect consumptions Appropriate energy saving measures should be taken to reduce vehicle fuel consumption and save non renewable materials or high energy consumption materials Moreover energy saving concept exists in the entire life cycle of a bridge energy efficient bridge engineering has a strategic significance of promoting sustainable development in highway transportation sector DEVELOPMENT STATUS OF BRIDGE ENGINEERINGPER Large scale bridge construction started from 1980s in China Till the end of 2009 China had 621 900 bridges in total surpassed USA in number and became the world s largest bridge country The construction of long span and super long span bridges had been the most significant mark of bridge construction progress in the past 30 years Half of the world s top 10 long span beam bridges arch bridges and suspension bridges are located in China and eight of the top ten long span cable stayed bridges lie in China Furthermore Donghai Bridge was opened to traffic in 2005 marked the start of constructing large cross sea bridges or cross river bridges after that Hangzhou Bay Bridge 36 kilometers and Zhoushan Peninsula Project 48 46 kilometers successively opened to traffic in 2008 and 2009 In addition 2889CICTP 2012 ASCE 2012 CICTP 2012 Downloaded from ascelibrary org by Changsha University of Science and Technology on 06 04 13 Copyright ASCE For personal use only all rights reserved Qingdao Gulf Bridge 41 58 kilometers and Hong Kong Zhuhai Macao Bridge 49 968 kilometers are under construction Bohai Bay Bridge Yangtze River Crossing Bridge project Zhujiang Lingdingyang Bridge Qiongzhou Strait Bridge and Taiwan Strait Cross sea Project have been planned already besides Within the first 20 years of the 21 century national highway network and rural road construction project will be put into practice in China Roughly 200 000 bridges with a total length of about 10 000 km will be constructed including approximately 100 grand bridges the total length of which each exceeds 400m However from experiences of the world projects carried out in rapid development period usually have poor quality Imperfections accompany with the whole process from design to construction and other sectors as a result insufficient performance and functional defect problems are often found At the same time currently the safety of nearly 100 000 bridges account for nearly 15 of the total number of bridges in China in the highway network of China are threatened by diseases including concrete cracking the corrosion of reinforcement the corrosion and degradation of cable the weakening of vibration fatigue and the corrosion of steel bridge The maintenance and repair of old bridges will become an inevitable choice to fulfill the sustainable development of highway transport which is determined by the characteristic of old bridges in China that is Chinese bridge has a big number base grows rapidly and suffered by problems left over by history With the construction of new bridges the maintenance of the old bridges will get into a peak period Both constructing new bridges and maintaining old bridges will waste a lot of energy According to some researches transportation is known to be a large consumer of energy resource and the fastest rising energy consumption sector Bridge is a key component of highway transportation energy problem accompanies with the whole course of the construction and maintenance of bridge furthermore this problem is one of the most significant sectors in the national economical energy saving Energy saving ranking first in the seven strategic new industries listed in the twelfth five year plan is an important concern of the growth of the national economy That s why the scientific concept of development and practicing the idea of energy saving are regarded as the guiding ideology and inevitable responsibility of bridge engineers On the basis of discovering problems in depth and strengthening energy saving awareness adopting feasible energy saving measures and enhancing management in the use of energy in the whole process of the planning design construction and maintenance of bridges is a key subject and mission of bridge engineering 2890CICTP 2012 ASCE 2012 CICTP 2012 Downloaded from ascelibrary org by Changsha University of Science and Technology on 06 04 13 Copyright ASCE For personal use only all rights reserved THE DEFINITION AND STATUS OF ENERGY According to the Energy Conservation Law of the People s Republic of China published in 2007 the term energy as used in this Law refers to coal crude oil natural gas liquefied petroleum gas biomass energy power heat and other resources from which useful energy can be derived directly or through processing or conversion At present the total energy consumption of China is about one third of that of U S accounting of about one tenth of that of the whole world and ranks second in the world However China s per capital reserves of coal petroleum and natural gas are below the world average level furthermore the energy intensity per capita in China is far lower than that in most countries and petroleum only accounts for 11 1 of the total amount of the whole world in particular Meanwhile the energy consumption per unit of output value in China is the highest in the world which is twice as much as that of the world average besides Furthermore at present the energy utilization ratio in China is only about 30 which is 10 lower than that of developed countries China is in a period of rapid industrial and urbanization development the situation of high energy consumption intensity accompanies with a continued expansion of consumption scale and an extensive mode of growth characterized by high investment high consumption and high pollution For the reasons cited above the contradiction between supply and demand of energy has been increased Problems in the supply and security of energy emerge and become a main restricting factor of the social and economic development in China Highway transportation plays a key role in the comprehensive system of transport and energy is the direct driving force to the growth of the construction and maintenance of highway transportation For this reason the shortage and irrational consumption of energy will doubtless affect the growth of highway transportation ENERGY PROBLEMS IN BRIDGE ENGINEERING 1 Vehicle Fuel Consumption Energy consumption in the highway transportation system mainly comes from road vehicles which could be classified as either direct energy consumption or indirect energy consumption Direct energy consumption refers to the part used to drive vehicles Indirect energy consumption refers to the energy used for maintaining and operating the transportation system which comprises the energy needed to repair vehicle maintain highway and bridge The technical condition of bridge construction is a significant factor that influences the vehicle fuel consumption ratio for bridge itself bears the weight of vehicle Vehicle fuel consumption is determined by the driving status of vehicle which is influenced by the technical condition of bridge such as average grade bridge deck surface roughness and so on Ba 2010 Compared to bridges in good technical condition 2891CICTP 2012 ASCE 2012 CICTP 2012 Downloaded from ascelibrary org by Changsha University of Science and Technology on 06 04 13 Copyright ASCE For personal use only all rights reserved bridges with large vertical slope and rough deck surface wastes more energy to carry the same traffic volume Furthermore rational design speed influences transport condition Researchers suggest that when the speed is lower than normal vehicle fuel consumption amount is markedly increased with the speeding down of vehicles In addition fuel consumption amount increases when vehicle is speeding up above normal speed Moreover traffic volume and traffic components are influenced by the width of bridge deck Ultimately vehicle fuel consumption amount is influenced Generally speaking mixed traffic with high traffic volume consumed more energy than unmixed traffic with low traffic volume For instance frequent starts and stops with vehicle an increase in the number of car braking and acceleration from stop and traffic congestion problems will all bring about high energy consumption amount Li 2009a Compared to normal condition energy consumption amount will increase by several times in these circumstances Du 2007 traffic congestion leads to transportation efficiency decrease which will increase the cost of urban development and in turn has a strong impact on the social and economic development of cities what s worse in this situation energy consumption and pollutant discharge grows Cai 2008 Maintenance and reinforcement are indispensable for ensuring the safe and natural service ability of bridge in operation period For instance the design reference period of cable stayed bridge is 100 years yet the design working life is only 25 to 30 years so cable replacement work is inevitable for cable stayed bridge and under current situation the implementing of most cable replacement work causes traffic to stop temporarily Therefore the maintenance and reinforcement of old bridge will cause temporary traffic conjunction and cars have to go around by roads which take much longer it will in turn increase traffic volume amounts and change transport conditions of neighboring roads and result in the increase of total fuel consumption amount and unit energy consumption of vehicle This energy constitutes a high proportion of the total energy used up in the life time of bridge Particularly the maintenance and reinforcement work of some large bridges are extraordinarily complicated and the construction time is nearly one year long in this instance the costs of maintenance and reinforcement are potentially enormous Therefore energy used for the maintenance and reinforcement of bridge is a continuing and lasting investment which is mainly reflected in vehicle fuel consumption Du 2007 2 Material Consumption Both the construction of new bridge and the maintenance and reinforcement of old bridge will waste plenty of material resources such as cement steel and so on which are non renewable and high energy consumption resources Strictly speaking energy is a kind of resources so energy is not equate to resources 2892CICTP 2012 ASCE 2012 CICTP 2012 Downloaded from ascelibrary org by Changsha University of Science and Technology on 06 04 13 Copyright ASCE For personal use only all rights reserved however the processing and production of materials used in constructing bridges waste lots of energy Take cement used for producing concrete for example primary raw materials for producing cement are limestone and clay Limestone and clay are broken milled and made into raw material and then raw material is put into a cement kiln to generate a kind of calcined product clinker aggregate which is mixed with plaster and milled that s the technological process of producing cement Statistics show 0 95 0 98 ton limestone is needed to produce 1 ton cement and limestone will be exhausted in 30 to 40 years Li 2009a Meanwhile coal is the main fuel for cement industry and a large amount of power is consumed for this reason cement industry is a typical big power consumer According to some statistics coal consumption of cement industry was 186 864 million tons in 2009 in China which accounted for 81 6 of the total coal consumption amount of building materials industry Meanwhile power consumption was 137 6 billion kilowatts which accounted for 65 4 of the total power consumption amount Take raw steel material for another example raw steel material includes steel steel stranded wire profiled bar and so on Iron and steel industry is a traditional big power consumer According to statistical results published in 2010 energy consumption amount of steel industry accounted for more than 15 of the total energy consumption amount of the whole country In the energy resource structure of steel industry the proportion of coal is 69 9 power is 26 4 petroleum is 3 2 and natural gas is 0 5 While in industrial countries power is above 30 petroleum and natural are 25 As a result of the special energy resource structure comprehensive energy consumption of ton steel of China is 15 to 20 kg t higher than other countries At present energy cost accounts for 20 to 35 percent of the total cost of production in steel industry At the same time in accompany with the processing and manufacturing of steel industrial wastewater effluent accounts for 8 5 percent of the total industrial discharge amount while industrial dust discharged accounts for 5 18 percent A survey of these building materials used in the construction and maintenance of bridge shows that energy consumption problem deserves attention The utilization of non renewable materials and high energy consumption materials contributes to energy consumption problems IDEAS AND MEASURES OF ENERGY CONSERVATION IN BRIDGE ENGINEERING According to the No 5 Year 2008 Order from the Ministry of Transport of the People s Republic of China the Implementation Approach of the Energy saving Law of China carried by highway and waterway traffic energy conservation means the strengthening of energy utilization administration in highway and water 2893CICTP 2012 ASCE 2012 CICTP 2012 Downloaded from ascelibrary org by Changsha University of Science and Technology on 06 04 13 Copyright ASCE For personal use only all rights reserved transport adoption of measures which are technologically feasible economically rational and bearable to the environment and society reduction in losses and waste in all links throughout the whole course of highway and water transport and more efficient and rational utilization of energy resources On the basis of the above energy problem analysis in bridge engineering sector energy conservation in bridge engineering should focus on saving vehicle fuel and reducing the utilization of high energy consuming materials and emphasize the importance of strengthening the energy utilization administration and increasing the efficiency of energy utilization Energy conservation idea and measures should run through the entire life cycle of bridge including primary stage plan design construction operation and maintenance Energy saving Plan 1 The Selection of Bridge Location On the premise of meeting the needs of route joints and structural design requirements the principle of minimum construction length need to be considered while determining bridge location so that the road haul could be reduced In addition the source of material and the convenience of material transport should be carefully considered On the one hand make the best of materials at the site of the bridge like stone and sand rock On the other hand the haul distance should not be too long so as to save fuel consumption in transport link 2 The Profile of Bridge and Grade of Deck The decision of profile of bridge should take the following factors into consideration that is geometric plane surface vertical section and transverse section so as to get a smooth going surface a balanced vertical section and a sound transverse section The key of applying energy saving idea is to strike a balance between the design of geometric plane surface and vertical section The grade of deck has a big influence on vehicle fuel consumption Vehicle fuel consumption grows geometrically with the grade of deck For saving energy reducing the grade of deck deserves prior attention However the reduction of grade often results in the increasing of plane line shape which leads to the increase of fuel consumption So the balance point of geometric plane surface and vertical section is minimum total fuel consumption This theory is of great importance in high grade highway yet less important in plain and hilly area 3 The Design Speed of Bridge The design speed of bridge is determined mainly by topography and geology along the line in addition to meeting the requirements of function grade and traffic flow of route However considering only the topography and geology condition often leads to reducing deign speed which will in turn places energy conservation in 2894CICTP 2012 ASCE 2012 CICTP 2012 Downloaded from ascelibrary org by Changsha University of Science and Technology on 06 04 13 Copyright ASCE For personal use only all rights reserved an unfavorable circumstance Generally speaking the design speed of vehicle is in direct proportion to energy consumption level of running vehicle That is higher of the design speed more remarkable of the energy saving effect For vehicle which is running on a bridge with lower design speed needs to accelerate and stop frequently which will increase fuel consumption Yet higher design speed can keep vehicle at best economic speed freely and lowest fuel condition So under like conditions higher design speed is preferred