Thursday, August 30, 2012

Disaster Resilience in Congress

Disaster resilience has recently caught the attention of the United States Congress. Representatives Davis (R-KY) and Diaz-Balart (R-FL) introduced a bill proposing tax credits for resilient construction. The bill refers to the FORTIFIED program by the Insurance Institute for Business and Home Safety.

In other action, the National Institute of Building Science recently provided testimony to the Congressional Transportation and Infrastructure Committee's Subcommittee on Economic Development. Intitute President Henry L. Green, Hon. AIA, reiterated that mitigation efforts save about four dollars for every dollar spent; argued for increased collaboration between federal agencies; and proposed suggestions for improved code development, adoption, and enforcement.

Article by Disaster Resilience Working Group web liaison Tonatiuh Rodriguez-Nikl, Ph.D., P.E. Check out other recent articles about disaster resilience.
Wednesday, August 22, 2012

Like a Radiator: Thermal Bridging

Some architectural gems have recently taken a lot of heat for loosing a lot of heat. Thermal bridging is a pervasive problem for all structures with monolithic slab cantilevering balconies. The authors of this article hosted at have turned their infra-red camera's on Chicago's iconic Aqua tower. Beyond simply highlighting shortcomings, some more efficient alternatives are proposed.

Link provided by committee member Kathrina Simonen, R.A., S.E, LEED-AP, assistant professor at the University of Washington.

Sunday, August 19, 2012

Sustainable Infrastructure Update

The recently revived Infrastructure Working Group (IWG) strives to engage the structural engineering community outside of building designers in an effort to disseminate the fundamental concepts of sustainability that are applicable to all types of structures.

While the LEED rating system has pushed building designers to develop and apply their fundamental principles of sustainability, the lack of such a driver within the bridge, tunnel, dam, levee, and other industries has left a gap in the sustainability fundamentals of its engineers. The IWG is working to fill that gap by raising awareness about sustainability project rating systems such as Envision and Greenroads that are applicable to transportation and other non-building type structures.

Envision is a newly released system developed to help evaluate the sustainability of civil infrastructure. It was created by the Institute for Sustainable Infrastructure (ISI) which was founded by the American Society of Civil Engineers (ASCE), the American Council of Engineering Companies (ACEC), and the American Public Works Association (APWA). The rating system uses a holistic approach to educate owners and project teams on the aspects of sustainability and offers guidance on how to ensure each aspect receives due consideration. Projects are evaluated based on 55 credits within 5 categories: Quality of Life, Leadership, Resource Allocation, Natural World, and Climate and Risk.

More information about Envision and ISI can be found at

Post submitted by committee member Marty Chorkey.
Wednesday, August 15, 2012

10 Steps to Greener Concrete


According to the World Business Council for Sustainable Development (WBCSD), “concrete is the most widely used material on earth, apart from water, with nearly three tons used annually for each man, woman, and child.” Most structural engineers are familiar with efficient design practices for working with concrete, but there are sustainable considerations that should also be taken into account. There are at least three areas in which the characteristics of concrete can be used sustainably:

1.     Exposed concrete can be used as both an interior or exterior finish, thereby reducing the additional material cost of cladding, painting, installing drop ceilings and sheeting, etc.
2.     Concrete structures intrinsically have more thermal mass – a property that enables heat energy to be absorbed, stored, and later released, giving greater comfort in the both the heat of summer and the cold of winter.
3.     Carefully considered mix designs can reduce the embodied carbon intrinsic to concrete, improve long-term durability, and still provide sufficient workability.

Unfortunately, the production of portland cement releases a high volume of carbon. Approximately 40% of embodied carbon is associated with powering the extremely hot furnaces needed for the transformation. Cement manufacturers are experimenting with ways to become more efficient. (4) Structural engineers can specify that cement be sourced from plants scored by the Energy Star Industrial Focus Program with an Energy Performance Indicator (EPI) above 75.

The remaining 60% of embodied carbon in cement is a result of calcination, the intrinsic chemical reaction whereby limestone is transformed into clinker, on the way to becoming cement. Therefore, the primary means of greening concrete is to reduce the amount of portland cement in the mix.

Fortunately structural engineers can have great control over the mix designs selected. Some relatively simple steps can be taken to ensure that more sustainable concrete mixes are used on your job site. These can be simplified into four rules of thumb: (5) reduce water content, (6) use complimentary cementitious materials (CCMs), (7) use the maximum aggregate size, and (8) specify proper strengths.

Reduce water content. Keep the water/binder ratio low, and although less cement is used, the same strength can be achieved. A low w/b is also good for durability. Based on the relationship of specific gravity between concrete and water, a w/b ratio greater than 0.32 is most likely to result in free water that is not bound to the binder paste. This results in unwanted voids and drying shrinkage as the free water evaporates (instead of being consumed in the chemical reaction).

High slump is often desirable for workability. (9) Fly ash and superplasticizers help improve workability without increasing water. The spherical shape of fly ash acts as a physical lubricant and thus aids in cement hydration. Water-reducers likewise increase slump, however, too much of these admixtures can cause segregation and excessive bleed water. A good rule of thumb is to limit the water-reducers or superplasticizers to 2 percent of the mass of the binders.
Fly Ash (Meryman 2007)

Use complimentary cementitious materials (CCMs). Fly ash, slag, natural pozzolans, and ultrafines can be used in lieu of portland cement. Many such materials have less embodied carbon or are recycled industrial byproducts. The basic chemical reaction between portland cement and water produces calcium hydroxide (CH).  Many CCMs then react with the CH to produce calcium silicate hydrate (C-S-H), which provides a much stronger bond, particularly around the aggregates.

With regard to durability, C-S-H is known to be a much denser product and therefore less permeable. Non-cement binders also tend to reduce the heat of hydration. Although specific alkali-silica reactions are known, CCMs generally enhance both strength and durability. (10) For a more in-depth analysis of durable mixes, designers can utilize the Life-365 freesoftware from the National Ready Mix Concrete Association (NRMCA).

Use the maximum aggregate size. This reduces the surface area that the binder paste needs to cover thereby keeping the past volume lower. Normally available aggregates are stronger than the surrounding hardened paste.

Specify proper strengths. Choose target strengths at ages that realistically reflect the needs of the project. Recall the above described chemical reaction involving CSMs: C-S-H takes longer to develop and the conventional 28-day period may not be sufficient. If possible, specify 56 or even 90 day strength. This gives mix designers at the batch plant more freedom to utilize some CCMs.

The above recommendations were sourced from SustainabilityGuidelines for the Structural Engineer, Chapter 3.2 – Concrete. Current and former SEI Sustinability Committee Members influential in authoring the referenced chapter include: Helena Meryman, Sarah Vaughan, Alan Kren, and Iyad Alsamsam. This summary is by Ken Maschke, P.E., S.E., LEED A.P., associate with Thornton Tomasetti in Chicago, IL.
Saturday, August 11, 2012

Life Cycle Assessment

The Life CycleAssessment (LCA) Group is working toward educating structural engineers on the meaning and professional application of LCA criteria, procedures, and measurements in order to make environmentally conscience decisions on the use of structural materials.

Life cycle assessment (LCA) is a method of measuring the total environmental impact of a product or process, from acquisition of raw materials to end-of-life.  For structural materials, the life cycle generally includes extraction, manufacture, transport, construction, maintenance, re-use and recycle opportunities and end-of-life including demolition and disposal. Thus LCA provides the most complete picture of environmental effects inherent to choosing certain structural materials.  It is analogous to performing environmental accounting on the structural materials in order to choose the most environmentally friendly design solution over the anticipated standardized life of such materials.

LCA has four basic stages or evaluation components; goal and scope definition, inventory analysis, impact assessment, and interpretation.   The inventory analysis can utilize such catalogs as the U.S. Life-CycleInventory Database prepared by the National Renewable Energy Laboratory, and the Inventory of Carbon and Energy ('ICE') prepared by the University of Bath.  The analysis can be done in software programs such as Athena Eco-Calculator and the SimaPro.  In addition, some companies are coming out with their own proprietary software for post processing the data and inventories based upon specific circumstances. 

LCA assessment tools move beyond simplistic assumptions and determine true environmental impacts.  Measurements of LCA include multiple metrics including quantifying the environmental ‘costs’ (e.g. CO2emissions) of each item, the energy required to produce the items (embodiedenergy) and various measurements of how these impacts relate to larger scale environmental concerns (e.g. global climate change)

The main goals of the group include:

1.   Providing information and resources to the structural engineering community on applications of LCA in building and infrastructure design. 
2.   Improving LCA software to better represent environmental impact reductions we know can be made from structural design and specification.
3.  Engaging structural engineers in the incorporation of LCA into green building and infrastructure rating systems and building codes.

Currently, the group is working on publishing their response to the top 10 most encountered questions, as experienced by LCA Committee members within their practice of structural engineering.
Wednesday, August 8, 2012

Thermal Breaks for Brick Shelf Angles


The Brick Industry Association (BIA) has an article in their most recent issue of Brick in Architecture magazine which includes information and detailing of thermal breaks for brick shelf angles in veneer construction over cold-formed steel.  

The article begins on page 9; the section entitled “Thermal Design” begins near the end of page 13, and the details are on pages 12 and 13.
BIA has recommended that AISI reference this article in their upcoming rewrite of the steel stud brick veneer design guide; I found out about it in a memo received this morning with a BIA review of the old design guide.
Provided by committee member Don Allen, P.E.
Friday, August 3, 2012

Carbon White Paper Coming Soon

The committee’s Carbon Working Group white paper, "Structure and Carbon: How Materials Affect the Climate" will explore how carbon dioxide and other emissions contribute to climate change, how the manufacturing of the structural materials in buildings creates such emissions, and the ways that structural engineers can make changes in their current practice to reduce greenhouse gases.  In a nutshell, we aim to quantify the carbon footprint of structure, and provide tools for designers to reduce it.

The paper covers the modern structural materials: concrete, steel, masonry, wood, and fiber-reinforced polymers. Carbon footprint data is based on life cycle assessment research conducted for industry trade groups and research consortiums such as AISC, PCAAthena, and CORRIM. In addition to reporting raw emission numbers, we show how the data can be used to study material optimization on an example floor plate.  We also discuss uncertainty in the data collected, to make users aware of current limitations and to promote further study.

"Structure and Carbon: How Materials Affect the Climate" is in its final review phase. Look for its public release on this website later this year.

Post by Carbon Working Group liaison, Adam Slivers, P.E., S.E., Associate at KPFF Consulting Engineers in Seattle, WA.

Wednesday, August 1, 2012

Gray to Green: How to Make Cleaner Concrete

Sustainable concrete has captured the imagination of always provocative Popular Mechanics. A recent web article explores radical new ways to green concrete. Most structural engineers are well versed in supplemental cementitous materials like fly ash and blast furnace slag, but have you considered rice husks, sewage sludge, and geopolymers? The article also suggests using prcelain from recycled toilets for aggregate and hempcrete blocks as an alternate to CMU. Finally, a PM article wouldn't be complete without some exploration of space. Strategies are discussed for converting moonrocks to traditional or sulfur-based concretes.
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