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Effective contribution of structural engineers to green buildingsand sustainabilityTariq Chaudhary and Awais Piracha

Abstract: Structural engineers are key players in architectural or civil infrastructure projects. However, their contributionseems to be limited in sustainability rating systems. This review analysed the credits available in the Leadership in Energy andEnvironmental Design green building rating systems related to the structural aspects. It concluded that the points related to thestructural aspects are proportional to the cost of structural elements in a building. Embodied and total energy requirements oftypical buildings were examined and it was determined that the embodied energy in the structural components has a shareranging from 2% for traditional buildings to 25% for net zero buildings. Structural strategies that can enhance sustainability butare not included in the rating systems were discussed. Enhancing structural resilience to natural andman-made disasters will bethe most significant contribution of structural engineers to sustainability.

Key words: sustainable development, structural engineer, rating systems, green buildings, embodied energy, LEED, disasterresilience.

Résumé : Les ingénieurs de structures sont des joueurs clés des projets d'infrastructure architecturale ou civile. Mais leurcontribution semble être limitée pour les systèmes de cotation de la durabilité. La présente revue analyse les crédits disponiblesdans les systèmes de cotation de bâtiments verts LEED en ce qui a trait a la structure. Elle conclut que les points ayant trait auxaspects structuraux sont proportionnels au coût des éléments structuraux d'un bâtiment. Les exigences en énergie grise et totaledes bâtiments typiques sont étudiées et il a été déterminé que la part de l'énergie grise des composants structuraux variait de2 % pour les bâtiments traditionnels jusqu'a 25 % pour les bâtiments a consommation énergétique nette zéro. Les stratégiesstructurales pouvant améliorer la durabilité, mais qui ne sont pas incluses dans les systèmes de cotation, sont discutées. Lacontribution la plus significative des ingénieurs de structures envers la durabilité sera sans doute l'amélioration de la résiliencestructurale contre les catastrophes naturelles et causées par l'homme. [Traduit par la Rédaction]

Mots-clés : développement durable, ingénieur de structures, systèmes de cotation, bâtiments verts, énergie grise, LEED, résiliencecontre les catastrophes.

1. IntroductionBuildings are major consumers of natural resources, potable

water, and energy (40% of the total) on the one hand and contrib-utor to global green-house gas (GHG) emissions on the other(UNEP 2009). A major reduction in global GHG is not achievablewithout a significant decrease in contributions from the buildingsector. Therefore, the Sustainable Building and Climate Initiative(SBCI) of United Nations Environment Program (UNEP) pushedfor reduction in emissions from buildings into a global strategyto tackle climate change at the United Nations Climate ChangeConference — COP15 held in Copenhagen in 2009 (UNEP-SBCI2009).

In recent years, the popularity of green building rating systemshas grown considerably. Weisenberger (2011) pointed out thatwhile overall building construction in recent years has declined,the demand for green buildings has dramatically increased from2.5% in 2005 to 32% in 2010 in the USA. Weisenberger also pointsout that the contribution of structural engineers in green buildingdesign is limited to specifying the construction materials. Heechoes Kestner et al (2010) when he encourages structural engi-neers to seek a bigger role for themselves in the green buildingrating system. Watermeyer and Pham (2011) presented a generalsustainability framework in which structural engineers not onlyhave to design new structures according to the current building

codes and standards but also have to assess the fitness of use ofexisting building stock. Danatzko and Sezen (2011) have elabo-rated sustainable structural design strategies and methodologiesindependent of the green building rating systems.

This paper focuses on examining the responsibilities entrustedto structural engineers in the context of sustainable design in theLeadership in Energy and Environmental Design (LEED) (USGBC2009) rating system. Credits related to the structural trades in theLEED rating system are examined in section 2. Section 3 of thepaper deals with energy considerations for structural engineers inthe context of green building design. The structural engineeringpractices that make positive contributions to sustainability butare currently not included in the rating systems are examined insection 4. Conclusions of the review are presented in section 5.

2. LEED and structural engineersParticipation of structural engineers in the sustainability ef-

forts are examined in this section based on the relative cost ofstructural items in building construction and credits related tothe structural components in the LEED rating system.

2.1. Structural cost of a buildingTable 1 presents an estimate of structural cost for various build-

ing types (Taghavi and Miranda 2003; Design Cost Data 2012). The

Received 24 April 2012. Accepted 17 November 2012.

T. Chaudhary. Al-Imam Mohammad ibn Saud University, P.O. Box 84937, Riyadh 11681, Saudi Arabia.A. Piracha. University of Westerm Sydney, Sydney, Australia.

Corresponding author: Tariq Chaudhary (e-mail: mtariqch@hotmail.com; mtchaudary@imamu.edu.sa).

97

Can. J. Civ. Eng. 40: 97–100 (2013) dx.doi.org/10.1139/cjce-2012-0154 Published at www.nrcresearchpress.com/cjce on 19 November 2012.

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structural cost as a percentage of the total building cost variesbetween 8% for healthcare projects and almost 50% for pre-engineered warehouse buildings.

For a typical office building in North America, the constructioncost breakdown is as follows: 35% (architectural), 25% (mainte-nance enforcement program; MEP), 18% (structural), 12% (interi-ors), and 10% (civil). The bulk of the cost is related to thearchitectural and MEP aspects (60%) while structure's share isabout 18%.

2.2. Credits related to structural components in LEEDThe materials section in the rating systems contains credits of

interest for structural engineers. This section represents about15% of the overall credits in LEED. Credits in LEED are divided intothree categories based on involvement of structural engineers: (a)direct involvement, (b) indirect involvement, and (c) supportingrole.

2.2.1. Direct involvementDirect involvementmeans that structural engineers are directly

responsible for specifications and design of the structural ele-ments related to these credits. About 16% of the LEED credits fallunder this category of which most significant are building reuse(MR c1.1) andmaterial reuse credits (MR c3). Unfortunately, both ofthese credits are costly to achieve and historical data indicate thatthese credits have been attempted in only 5% and 6% of the proj-ects, respectively (Matthiessen et al. 2004).

Credit MR c4 (recycled content), is a popular one and has beenattempted by 95% of the LEED registered projects. The commonroute of achieving this credit is to specify supplemental cementi-tious materials (SCM) to replace cement content in concrete andto exploit the use of scrap in the manufacturing of steel. Steelcontains up to 90% recycled content in its manufacturing. As re-cycling is a well-established practice in the steel manufacturingindustry, therefore the credit related to the use of recycled mate-rials is achieved without additional reduction in GHG emissions.

Structural engineers caneffectively specifyproducts that aremadeof rapidly renewable materials (MR c6) but have performance equiv-alent to the conventional products. For example, floor joists, curtainwall, and scaffolding made of laminated veneer bamboo (LVB) in-stead of traditional wood species (Lamboo 2012).

2.2.2. Indirect involvementIndirect involvement means that the choice of structural sys-

tems and (or) materials has an impact on the performance ofbuildings and on achievement of sustainability credits in othercategories. About 18% of the LEED credits are included in thiscategory. The most important LEED credit in this category isEA c1 — optimize energy performance. The base building for en-ergy calculations in ASHRAE 90.1 is a light weight assembly con-sisting of a steel stud and batt insulation envelope. This basemodel is inherently less energy efficient due to thermal bridgingprovided by steel studs as compared to the envelope comprising ofinsulated precast concrete panels or insulated masonry walls. Useof these options can contribute up to 19 points to the LEED score-card and at the same time result in an energy saving of up to 40%(Zechmeister 2008).

2.2.3. Supporting roleStructural engineers can play a supporting role in achieving

LEED credits related to sustainable sites, water efficiency, energy,

and atmosphere and indoor environmental quality credits. In sup-porting roles, structural engineers provide technical expertise bydesigning the pertinent structural elements like rainwater stor-age and wastewater treatment tanks (water efficiency credits),support for solar panels and wind turbines (onsite renewable en-ergy credit), support for light shelves and other day-lighting tech-niques (indoor environment credit). These efforts can help inapproximately 20% of the LEED credits.

2.3. How enthusiastic are structural engineers aboutsustainability?

The recent surge of sustainable rating certifications has alsogenerated the demand for qualified design and constructionprofessionals, like UGBC's LEED Accredited Professional (LEED AP).Currently, there are more than 150 000 LEED APs of which 31%are architect, 18% construction managers, 7% Mechanical andServices engineers, and 6% interior designers. Only 2% of theLEED APs are structural engineers, which is an indication thatstructural engineers are not enthusiastic about sustainabilityas defined by LEED.

2.4. DiscussionThe allocation of points related to the structural trades in the

LEED rating system (16% for direct involvement and up to 54% ifindirect and supporting roles are also included) are in line withthe percentage cost of structural components in buildings (18% foroffice buildings). However, participation of structural engineersin the green building design process is lacking as only 2% of theLEED AP are structural engineers. This low number is not at parwith the relative importance of structural engineers in the overallprocess of building design and construction when measured interms of project cost or points in the LEED rating system. Thisanomaly can be attributed to the following reasons:

• Limited role of structural engineers in conception, planning,management, and execution of building projects whencompared to architects, construction managers, and MEPengineers.

• Small impact on cost savings due to adoption of sustainabilitymeasures in structural items. For example 30% cement replace-ment with fly ash results in less than 0.03% of overall construc-tion cost savings for an all-concrete building.

• University courses for structural engineers contain very littlecontent on sustainability and environmentally responsible de-sign practices.

• Lack of guidance from professional structural engineering bod-ies can be another reason for dearth of awareness among struc-tural engineers on this issue. The sustainability guidelines forstructural engineers produced by the Structural EngineeringInstitute (SEI) of ASCE (Kestner et al. 2010) and the report by theInstitution of Structural Engineers (IStructE 2012) have tried tofill this gap to some extent. However, both documents lack anindependent stance on sustainability and are more alignedwith the guidance provided by the green building ratingsystems.

3. Energy considerations for structural engineersTo effectively understand and tackle the underlying principles

of sustainable development, it is necessary that the impact of astructural engineer's design be defined in terms of embodied en-ergy, operating energy, and total energy. Embodied energy of a

Table 1. Structural cost for various building types.

Building typeOffice(a)

Residential(a, b)

Health care(a)

Educational(b)

High rise(a)

Industrial(b)

Warehouse(b)

Structural cost (%) 18 13 8 12 25 30 50

Note: (a) Taghavi and Miranda 2003; (b) Design Cost Data 2012.

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building is the energy required to build it. Cole and Kernan (1996)estimated that for a typical office building, its various compo-nents are: structural works (24%), envelope (26%), finishes (13%),construction (7%), services (24%), and site work (6%). Structuralcomponents comprise about 25% of the total embodied energy ina buildingwhile occupying 80% of itsmass. The share of embodiedenergy in the structural components is more than the cost ofthese items (refer to Table 1) due to the energy intensive processesrequired formanufacturing ofmain constituents of the structuralcomponents (i.e., steel and concrete).

Operating energy of a building is dependent on the type ofbuilding (i.e., traditional, energy efficient or high performance,passive or net zero), its design life, and the climate. Total energy isthe sum of embodied energy and operating energy. Sartori andHestnes (2007) provided a comparison of operating and total en-ergy required for various types of buildings located in cold climatewhere major expense of energy is related to space heating. Theyconcluded that share of embodied energy is 7%, 15%, 32%, and 100%of the total energy in traditional, energy efficient, passive, and netzero buildings, respectively. Respective share of embodied energyin the structural components is 2%, 4%, 8%, and 25% of the totallifetime energy use.

There is little incentive in reducing the embodied energy instructural components for ordinary buildings due to its miniscule2% share in the lifetime energy requirements. However, due totechnological advancements in energy efficient building envelopeand mechanical equipment, environmental awareness and gov-ernment regulations, energy efficient and net zero buildings andcommunities are being planned in various parts of the world. Theshift will enhance the importance of embodied energy in thebuildings and will provide structural engineers a chance to beresponsible for efficient design of 20%–25% of the total energy of abuilding.

4. Structural strategies that can enhancesustainability

Based on the conclusion of section 3 above, it is suggested thatthe structural engineers shall take active part in sustainabilityinitiatives without worrying too much about the points in therating systems. The following strategies are currently not allo-cated any weightage in LEED but can have a far reaching impacton the sustainable performance of buildings.

4.1. Baseline material usageThere is no baseline material use or structural form model for

structural efficiency as compared to the baseline for water andenergy use against which the efficiency of these items is mea-sured. Studies by Collings (2006) and Buckley et al. (2002) arepreliminary examples in this regard for bridges and buildings,respectively.

Adoption of this measure will give incentive for using less ma-terials and conserving natural resources. Strategies include: thinshell structures, bubble deck for reducing concrete volume, cas-tellated steel beams, post-tensioned concrete structures, highstrength materials etc.

4.2. Structural robustness and resilienceNatural disasters like floods, hurricanes, and earthquakes are

responsible for multi-billion dollar damage to buildings everyyear. Current building codes are formulated for life safety only inthe case of extreme natural disasters. This philosophy can resultin lack of resilience and robustness in the structures, which is themain reason for the widespread damage to structures. Addition-ally, with the adoption of probability-based ultimate strength de-sign in most building design codes since the early 1980s, the extramargin of safety that was present in the simplified working stressmethod has been taken away (Ellingwood et al. 1980). This fact can

be attributed to the disproportional loss and damage to buildingsand houses built after 1980s in the aftermath of recent naturaldisasters in the USA (Frank 2012; Pielke et al. 2008). Structuralengineers have started to address the shortcomings of probability-based design approach and are moving towards a philosophy thatis based on: ‘to protect against which is possible beyond what is probable’(O'Rourke 2012).

The most significant contribution from structural engineers tosustainable development will be improvement of current build-ing design codes to deliver more robust and disaster resilientstructures. This can result in structures with higher initial costand embodied energy and may require incorporation of new con-struction technology. Such a move will need the backing of theowners and the society.

Performance based design for sustaining the brunt of seismic,blast, and hurricane loads is one such methodology that is cur-rently available and has been put into limited practice in someregions (Fardis 2010). This methodology should be rewarded withsustainability credits as such structures have the capability ofreducing the wastage of embodied energy that will be spent onrebuilding of damaged and (or) collapsed structures.

4.3. Structural adaptability and reuseCredits related to reuse of existing structural components are

available in LEED. However, these are perceived as expensive cred-its and have been very infrequently attempted. A survey of demol-ished buildings in the USA found that more than 80% of thebuildings were demolished due to area redevelopment, lack ofmaintenance, or lack of adaptability for the new intended use(O'Connor 2004). Almost 40% of the new construction that willtake place in the US between 2000 and 2030 will consist of newstructures built after demolition of existing ones (Nelson 2004). Insuch cases, the embodied energy in the existing structure will belost. Similarly, the trend of shorter life spans of structures alsoresults in a higher embodied material energy per year. There is aneed to reverse this trend and adopt measures in the buildingcodes and sustainability rating tools that encourage longer designlives and reuse of structures.

Designing for easy deconstruction and reuse should be re-warded with more credits in the rating systems and more empha-sis shall be on reusing the structural components instead ofrecycling (CSA 2006; Webster and Costello 2002). Structural engi-neers have a major role to play in the deconstruction activity forthe purpose of safely and efficiently salvaging material and com-ponents for reuse or recycling (CSA 2012).

Related to adaptation and reuse is the issue of conservation,refurbishment, and restoration of existing structures to extendtheir service life and to save them from being demolished. Theexpertise of structural engineers is the most valuable in realizingthe aims of this objective.

4.4. Structural durability and longevityExtending the service life of a building is very helpful in achiev-

ing the sustainability goals as it reduces the share of the embodiedenergy per year of building use. Therefore, designing buildings fordurability and longevity is an important structural attribute thatshould be rewarded in the rating systems.

O'Connor 2004 has argued that the current structural design ofbuildings provides enough durability for intended design life of50 years. Analysing building demolitions he discovered that only5% of the buildings were demolished due to deficiencies in thestructural systems. Structural durability is often more of an issuefor bridges and other civil structures where the structural systemis exposed to the elements without any protection. However, evenfor the bridges, the average age at replacement is 68 years; whichis more than the design life of 50 years (Bettigole 1990).

Currently, durability of building facade and structural compo-nents is more of a maintenance issue than that of structural

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integrity. As longevity is a desired sustainability attribute, struc-tural solutions need to be formulated to enhance it. The aspect oflongevity, however, will have to address revised environmentalloads for a longer design life.

5. ConclusionsStructural engineers traditionally have not identified them-

selves with sustainable design. Growing concern for sustainabilityand increasing importance of green building rating tools haswarmed the structural engineers to LEED and sustainable designpractice. Structural engineers' first instinct seems to be catch-upon participation in these rating systems as well as criticism ofthese systems for not fully capturing structural engineers' role.

It must be understood that the current green building ratingsystems make very limited overall contribution to the goal ofenvironmental sustainability. Attaining even the highest LEEDPlatinum level for a building results in a GHG emission reductionof only 10%–15% (Brown and Southworth 2006). Structural engi-neers have to make thoughtful and carefully crafted contributionto sustainability without overly worrying about their role in thegreen building rating systems.

The following conclusions are drawn from this review:

1. Structural engineers are continuously involved with buildingsduring their life span and they need to be a part of the sustain-ability team as well. However, they need to define their ownguidelines for sustainable design without being overly con-cerned with points in the green building rating systems.

2. The share of responsibility given to structural engineers in theLEED rating systems is roughly proportional to the share ofthe structural components in the total cost of buildings.

3. For energy efficient, passive, and net zero buildings, the shareof embodied energy increases to 50%, 70%, and 100% of totalenergy, respectively. This implies that the importance of struc-tural embodied energy will grow in the future as buildingcodes mandates energy efficient and net zero buildings.

4. Structural robustness and resilience, structural adaptabilityand reuse, and structural durability considerations can havehigh impact on reduction of embodied energy and thus oughtto be included in the sustainability rating systems.

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