Thursday, July 20, 2017

Carbon Group Post 3: How Supplementary Cementious Materials (SCMs) Can Reduce Embodied Impacts of a Concrete Building

0 comments
This is the third in a planned series of blog posts on topics that are discussed in depth in the SEI Sustainability Committee’s forthcoming technical report, Building Structure and Global Climate, due out later this year.

In this example, a cradle-to-gate LCA was conducted to determine the embodied impacts of concrete on a building to compare the Global Warming Potential (GWP) of a reference building using typical concrete mixes with moderate amounts of Supplementary Cementitious Materials (SCMs) such as fly ash and slag and a proposed building using concrete mixes that have relatively high volumes of fly ash and slag. The building is an 18 story residential tower located in the northeast United States. Compressive strengths for each structural element are identified in Figure 1.


Figure 1. Specified compressive strength of concrete for an 18 story residential tower.

The first step in the analysis is to identify typical concrete mixes for the reference building. In 2014 (updated in 2016), National Ready Mixed Concrete Association (NRMCA) published benchmark mix designs and their environmental impacts for eight different regions in the United States (www.nrmca.org/sustainability). This example uses the benchmark mix designs for the Northeast region. 
The next step is to estimate mix designs that have significantly lower GWP than the benchmark mixes that still meet the performance criteria (strength, durability, etc.). This example uses high volume SCM mixes from the NRMCA Industry-Wide Environmental Product Declaration (EPD). A summary of the concretes selected for the reference and proposed building are provided in Tables 1 and 2.

Table 1. Mix designs selected for the reference building (from NRMCA benchmark report)

Concrete Element
Specified Compressive Strength (psi)
Portland Cement (lbs/yd3)
Slag
(lbs/yd3)
Fly Ash
(lbs/yd3)
SCM content
Mat Foundation
6000
782
119
82
20%
Basement Walls
5000
741
112
78
20%
Floors B2-1
5000
741
112
78
20%
Floors 2-18
5000
741
112
78
20%
Shear Walls
6000
782
119
82
20%
Columns
8000
967
147
102
20%

Table 2. Mix designs selected for the proposed building

Concrete Element
Specified Compressive Strength (psi)
Portland Cement (lbs/yd3)
Slag
(lbs/yd3)
Fly Ash
(lbs/yd3)
SCM Content
Mat Foundation
6000 psi
256
342
256
70%
Basement Walls
5000 psi
242
323
242
70%
Floors B2-1
5000 psi
512
0
341
40%
Floors 2-18
5000 psi
581
0
249
30%
Shear Walls
6000 psi
427
256
171
50%
Columns
8000 psi
503
302
201
50%

Using the Athena Impact Estimator for Buildings (Athena IE) software, the reference building and proposed building were defined using the proposed mixes in Table 1 and 2 respectively. Athena IE has the NRMCA benchmark mixes and the NRMCA Industry-Wide EPD mixes pre-loaded into the software. The software also permits the user to define new mixes based on the existing mixes in the library or completely new mixes if that information is available from a concrete producer.

Once all the concrete information is defined for each project, the user can then run a report that will provide the estimated GWP, along with other impacts, for each building. The reference building will represent the largest impacts and the proposed designs will represent lower impacts. The results for this example showed that the reference building has a GWP for concrete of 6.14 million kg CO2 while the proposed building has a GWP for concrete of 3.92 million kg CO2 meaning that the high volumes of fly ash and slag mixes resulted in 36% reduction in GWP.


Keep in mind, this is example was simplified for illustration purposes. It only considered the effects of concrete during the material extraction and manufacturing stage on the environmental impacts of the building. The Athena IE software does contain environmental impact information for most materials and products used in buildings and allows input of operational energy data for conducting a more comprehensive whole building LCA.
Read more...
Thursday, June 15, 2017

Carbon Group Post 2: What About the Data?

0 comments
Carbon Group Post 2: What About the Data?

This is the second in a planned series of blog posts on topics that are discussed in depth in the SEI Sustainability Committee’s forthcoming technical report, Building Structure and Global Climate, due out later this year.

As with all analyses, the quality of environmental assessment results depends greatly on the quality of the input data. What we learned in our earliest structural engineering and computer programming courses holds true: garbage in = garbage out. When it comes to environmental analyses of our structures, no matter the level of detail of the analysis—carbon dioxide equivalent footprint (carbon footprint), life-cycle inventory, or life-cycle analysis (LCA)—quality input data is important to achieve credible, verifiable, and consistent results.

Uncertainty in analyses related to data quality and variability is important enough that an entire chapter of the SEI Sustainability Committee’s forthcoming technical report is devoted to the topic. In this post, I’ll highlight the key questions to ask related to data when evaluating a carbon footprint.

Data quality and variability
When performing a carbon footprint, data typically can be taken from a few different types of sources:
·         Public databases
·         Private databases
·         Primary data
A public database is usually managed by an association or a public or private institution. In the U.S., one public database is the U.S. LCI database and it is managed by NREL. Private databases can belong to large consulting firms that have performed multiple LCAs or software companies. Lastly, primary data can be obtained directly from product manufacturers. These data are the most applicable to the analysis, yet they are typically the most time consuming and expensive to get. In all cases, data for use in carbon footprint studies includes quantities of materials and energy that go into the system boundary being studied, and emissions to land, water, and air that come out of the system boundary.

Regardless of the source, data used in carbon footprints should be accompanied by evaluations of data quality and variability. Unfortunately, most LCI datasets do not include statistical variability. Information such as standard deviation and statistical distribution can be useful when evaluating or comparing carbon footprints. When evaluating an LCA report or EPD, research whether average data from public or private databases is representative of the industry. Keep relative uncertainty and statistical significance in mind when using data and results. Another way to check reliability of results is to request uncertainty/variability information from suppliers and trade organizations.

Data quality guidance is given in ISO standard 14044, Environmental Management-Life Cycle Assessment-Requirements and Guidelines. Typical factors that are addressed include: the timeliness, geographic and technical relevance, precision, completeness, representativeness, consistency, reproducibility, sources, and uncertainty of the information (for example, data, models, and assumptions).


This brief introduction to data quality and variability for carbon footprints will hopefully give you some indicators to look for the next time you read one of these studies. 
Read more...
Wednesday, April 19, 2017

Carbon Group Post 1: Why Climate Change Matters

1 comments
Structural Materials and Global Climate: Why Climate Change Matters

The Carbon Task Group of the Structural Engineering Institute’s Sustainability Committee has spent years studying the ways structural materials and systems affect climate change. This is the first of a planned series of blog posts on topics discussed in depth in our forthcoming technical report.

Why should we care about climate change? How bad could it be? Warmer winters will be nice, right?

We all know what’s happening. Among other things, people are burning a lot of fossil fuels—coal, oil, gas—sending unprecedented quantities of carbon dioxide and other greenhouse gases into the atmosphere. These heat-trapping gases are raising the temperature of our air and oceans, and increasing the ocean’s acidity. Polar ice is melting, contributing to sea level rise. Some regions are experiencing more intense storms and more frequent droughts. Coral reefs are dying. But so what, we can adapt, you might think. Well, maybe, but it would not be easy and the risks are great.

Even if you don’t live by the ocean or in a place where water shortages may become commonplace, there’s a lot to worry about. Climate change promises to be politically destabilizing, as millions of people find their homes inundated or food supplies threatened. They will need to resettle, increasing the flow of refugees. Political instability will lead to conflict, and yet more refugees. The Pentagon considers climate change a major risk, an “accelerant of instability” and a “threat multiplier.” We will all be affected.

And changes are coming fast. A recent study found that the United States is likely to reach an average temperature increase of at least 2°C by 2035, nearly 15 years earlier than the prediction for the globe as a whole, and that there’s at least a 50-50 chance that the northeast could reach this dubious milestone in only 10 years (Figure 1). Coastal cities such as Boston are talking about taking extreme measures to control advancing seas, such as constructing a four-mile-long, 20-foot high, barrier wall around the harbor to protect the low-lying areas of the city (Figure 2).

But the most unsettling changes are not inevitable. We still have a short amount of time to mitigate such worst-case outcomes, and structural engineers have a key role to play. We will explore what we can do in coming blog posts, so stay tuned.


Figure 1 shows the range of climate model predictions for the timing of temperature increases in the northeastern United States, the United States as a whole, and the world as a whole. The vertical axis represents the percentage of climate models that predict a given temperature will be reached by a given year.



Figure 2 shows a proposed 4-mile-long barrier wall to protect the city of Boston (Boston Globe, 17 February 2017).
Read more...
Monday, March 21, 2016

2016 Geo-Structures Presentations

0 comments

The ASCE-SEI Sustainability Committee and the ASCE Geo-Institute Sustainability in Geotechnical Engineering Committee had a very successful 2016 Geo-Structures Congress. We are happy to report that the two committees had representation at five sessions; they presented on various aspects of sustainable design. Since one of our main committee goals is to spread the word on sustainable design aspects that the practicing structural engineer can put to use, we’re posting the presentations here on our website. Have any questions on these presentations or on how to make your designs more sustainable, please comment below or contact Dave DeLong. Online copies of all of the following presentations are available here.

Track: The SEI Climate Action Initiative

‘Introduction/The Role of the Structural Engineer’ by Jim D’Aloisio

Raise awareness of the importance of climate change mitigation and adaptation by structural engineers, and share mitigation and adaptation ideas and strategies with the structural engineering community

’Mitigation of Emissions During Construction’ by Megan Stringer

My presentation discussed how engineers can quantify and reduce the embodied energy and emissions from buildings. 

‘Rationale for Concern’ byMark Webster

'Mitigation of Emissions During Building Operation'  by Dave DeLong

'The decisions that structural engineers make in detailing the building envelope can influence the building's R-value by a great degree. By detailing to increase this R-value, structural engineers can reduce the heating and cooling loads - and, as a result, the carbon impact - of the building over its service life

Track: Disaster Resilience – Indispensable for Sustainable Design

‘Introduction / Incorporating Life Cycle Assessment with Disaster Resilience’ by Tona Rodriguez-Nikl

An introduction to the session, putting forward the argument that disaster resilience must be considered as part of sustainable design. / A summary of recent efforts to integrate life cycle assessment with disaster risk methodologies. The goal of these studies is to quantify how different levels of disaster resistance affect environmental life cycle impacts.

‘Resilient Design Strategies for Structural Engineers

My presentation discussed resiliency, why it matters to structural engineers and how engineers can design resiliently. The presentation also reviewed current legislation, organizations, and rating systems that deal with resiliency. 

‘Learning to Survive: A global comparison of recovery from disasters’ by Erica Fischer and Sal Gimbert-Carter

Disasters have catastrophic impacts on countries economically, socially, culturally, and politically. This presentation compares how three different countries responded to three different disasters: 2004 Summatra Earthquake and Tsunami in Indonesia, 2005 Hurricane Katrina in New Orleans, and 2010-2011 Christchurch Earthquake Sequence in New Zealand.

 
Read more...
Monday, March 14, 2016

How do United States design codes incorporate disaster resilience and adaptation to climate change?

0 comments
In the United States, building codes govern the planning, design, construction and often operation of our buildings. Codes encompass sets of regulatory data that specify the minimum standards by which we must construct our building and non-building structures. The International Building Code (IBC) is widely used in the United States. It reflects a set of rules on how we should build and what type of techniques, materials and processes we should follow. The result is a safe and permitted structure. The IBC, however, does little to regulate building behavior with regard to disaster resilience and climate change adaption.


Disaster Resilience and climate change adaptation strategies are often implemented by choice from available disaster mitigation programs. These programs are categorically divided into voluntary and mandatory programs. Most, however, are voluntary. Elective programs encourage owners and communities to implement design choice that can reduce the risk of damage from natural disasters while mandatory programs seek to enforce and enhance standards through law. In the same way that governments adopt model codes as law (e.g. the IBC), mandatory mitigation programs provide language for state and local government and Federal Agencies to adopt as law with the objective of reducing losses from natural hazards. HPBRS (High Performance Building Requirements for Sustainability) is a mandatory program ready for adoption. Often such requirements are formatted to facilitate adoption as amendments to the current IBC. Still, such mandatory amendments need to be adopted by local and state officials for progress to be made. And even when done so, the increased disaster resistance and improved durability are considered enhanced sustainability requirements within such amendments.
 
Disaster mitigation programs for adoption are technically either prescriptive-based or performance-based. The simplest approach is prescriptive, where one specifies how to build using rules that engage the engineer with what the design must achieve, avoid and/or eliminate. Prescriptive guidelines are built upon assumptions about the nature of the hazard, the structural response, and the design objectives. Design professionals must carefully evaluate these assumptions again the objectives of the project before proceeding. Performance-based approaches state what the final results need to be and how it will be measured. It does not specify how those results are to be achieved. Such approaches can be achieved through probabilistic assessments of hazards and consequential damage whereby a cost-benefit analysis to balance increased costs with improved structural resistance is provided. The probabilistic process can be repeated to achieve varying levels of robustness. This can help optimize the balance between additional materials required for construction and probable savings from repairs during the facility’s lifetime. Despite superiority of the performance-based approaches, many of the programs discussed are prescriptive. They are relatively simple and therefore have greater likelihood of being adopted by owners and government agencies.
 

Much is happening to incorporate disaster resilience design strategies into standards and codes. Engineers continue to encourage the use of LEED and life-cycle assessment. A performance-based design standard for fire protection is to be published as a joint venture through the Fire Protection Committee of ASCE/SEI and NFPA. The AISC Design Guide 19 for fire design is also available. Other developments in FP can be found in ASCE/SEI/SFPE 29-05 Standard Calculation Methods for Structural Fire Protection 2005 and ACI 216.1-07 Code Requirements for Determining Fire Resistance of Concrete and Masonry Construction Assemblies, July 2007.
 
Established in 1969, the National Institute of Standards and Technology (NIST) Engineering Laboratory has for many years supported numerous national programs with the ultimate aim of identifying improvements in codes, standards, and practices. NIST supports the adoption of disaster risk management in the code and is currently funding researching in following topics:
 
  • Application of Database-assisted Design within the framework of the wind tunnel methods.
  • Risk Targeted Earthquake to replace the Maximum Considered Earthquake in an effort to make risk the common denominator in design, instead of hazard.
  • Structural load improvements.
  • Methods for estimating wind speeds based on the logarithmic law long.
  • Use of Saffir-Simpson hurricane scale for design wind speeds; database assisted design; and wind directionality effects.
  • In conjunction with NRC, criteria on hurricane-borne missile speeds.
  • Guidelines for including manufacturing into LCA.
Seismic events and weather-related disasters effect developed and developing countries, with much devastation faced by the rapidly growing low-income and lower middle-income countries (WBG, 2014). A lack of code compliancy along with failure to address issue of building and land-use regulatory policy in developing countries has lead to rapid urbanization without regard to disaster risk. The Global Facility for Disaster Reduction and Recovery (GFDRR), a World Bank-managed fund supported by 21 donor partners, the European Union, the World Bank, and the United Nations, is aiding in the provision of advanced knowledge and advice on disaster risk management. During the 2012-2013 fiscal year, GFDRR helped over 80 developing countries to better identify, prepare for, and recover from natural disasters (WBG, 2015). Assistance is provided across five areas: 1) risk identification; 2) risk reduction; 3) disaster preparedness; 4) financial protection for countries and people; and 5) resilient recovery when disaster does strike. The GFDRR aims to conventionalize disaster risk management and recovery into all country development polices and plans. A huge step towards this goal is the commitment of the International Development Association (IDA) to review all country strategies and operations for climate and disaster risks. (WBG, 2015).
 
Spending time and money up front to reduce the likelihood of loss during a natural disaster can bring significant benefits to owners and communities. These benefits are many and include lowering insurance costs, raising property values, providing security to residents, maintaining a consistent tax base, and minimizing the cost of disaster response and recovery. No community can ever be completely safe from all hazards, but resiliency planning gives communities the knowledge and abilities to protect themselves before and mend themselves after a disaster. Structural engineers and our supporting organizations play a vital role in resilient communities. As the nation moves forward to incorporate disaster resiliency as a national priority, standards organizations will be expected to play a critical and complementary role in achieving that goal.
References
Rodriguez-Nikl, T., Comber, M., Foo, S., Gimbert-Carter, S., Koklanos, P., Lemay, L., Maclise, L., VanGeem, M., and Webster, M. (2015). “Disaster Resilience and Sustainability”, SEI Sustainability Committee, Disaster Resilience Working Group, http://tiny.cc/DisResSust.


"Standards and Codes: Disaster-Resilient Structures and Communities." NIST. NIST Engineering Laboratory, 11 Jan. 2011. Web. 20 Oct. 2015.


“Improving Building Code Implementation and Compliance for More Resilient Buildings in Developing Coutnries: Considerations for Policy Makers.” The World Bank, October, 2014. Web. 21 Sept. 2015.
"Helping Countries Better Prepare for and Manage Disaster Risks, Climate Change." The World Bank, 30 January 2014. Web. 17 Sept. 2015.

Read more...
Wednesday, August 12, 2015

Hold Your Buildings to Higher Standards... of Resilient Design

0 comments
Building codes are modeled to safeguard public health and safety, not necessarily to limit damage or maintain a building’s function after a natural or man-made disaster. As a result, performance based design guidelines have been developed allowing structural engineers to design structures to a certain structural performance objective. This can include reductions in damage, repair costs and/or recovery time. Structures designed to perform to higher than code standards will typically require more materials and incur greater costs associated with design and construction resources (i.e. design time, construction time, and cost associated with both). These structures, however, have the potential to be more resilient during a disaster. The upfront costs associated with these structures can result in large monetary savings in the future. The project team should consider all of the benefits associated with a more resilient structure and decide if those benefits outweigh the upfront costs.

Monetary damages from natural disasters have seen significant increases over the last 5 years (Source: SEI Committee Report). Structural engineers should consider this when making the choice to design to higher standards. There is a vital need for resilient design with more people migrating to the coasts (where natural disaster hazards are greatest), and the economic value of possessions increasing substantially (Source: SEI Committee Report). Spending time and money up front to reduce the likelihood of loss during a natural or man-made disaster can bring significant benefits to owners and communities. These benefits include lowering insurance costs, raising property values, providing security to residents, maintaining a consistent tax base, and minimizing the cost of disaster response and recovery. 

Structural engineers must also take holistic design approaches because the interaction between structural and non-structural systems varies greatly. A system may require larger initial investments in materials and resources, but could have significant savings due to reduced damage of non-structural building components during a natural or man-made disaster, implying lower expected lifetime costs of the building.  

Designing structures for higher standards will typically result in additional upfront costs: both monetary and environmental. These costs should be considered throughout the life cycle of a building, especially for those structures at risk of natural and man-made disasters.  Hazard mitigation techniques typically come with significant benefits, and. implementing resiliency strategies will allow for better protection before and better recovery after an event.    
Read more...
Monday, June 22, 2015

What Do Structural Engineers Have to Do with Disaster Resilience and Climate Change Adaptation?

0 comments
Structural Engineers have the most direct impact on the disaster resilience of new and existing buildings and their ability to adapt with ever-changing climate. Although we typically cannot impact the location of a new structure, we can often impact its orientation, shape and exposure to various risks. The orientation and shape of the structure and the location of movement joints may significantly impact how much force is transferred to the building cladding, framing and lateral system during a severe wind event, earthquake, extreme temperature event, tidal event or terrorist attack. The first step in the process is to identify which risk factors pose a significant risk to the structure.

Structural Engineers must determine the potential risks for a given location over the service life of the structure even if this risk is not addressed by the governing code. For instance, current FEMA flood elevations do not directly factor in the impacts of future sea-level rise; depending on the service life of the structure, this may have a significant impact on the building’s exposure risk. We must first determine what code-prescribed requirements apply for addressing these various disaster risks, based on the occupancy type and importance of the structure. Some questions that need to be addressed are as follows:
  • What design codes are currently available for addressing that specific risk?
  • Do these codes specify loading and serviceability requirements?
  • Where codes or design aides are not yet available, what design practices can be implemented to help address this risk?
  • Building codes represent minimum/baseline requirements. Are these sufficient for the structure given its location?

After the various risk factors have been identified and the magnitudes of forces to be applied to the structure are understood, the Structural Engineer must then select the proper structural system and determine how the exterior cladding is anchored and transfers forces back to the structure. Below are some items to consider in this exercise:
  • Building Material Type: Structural steel, reinforced concrete, wood, masonry, light gage, etc.
  • Lateral System Type: Load-bearing or non-load bearing shear walls, moment frames, braced frames, dual systems, etc.
  • Level of Ductility: Response Modification Coefficient (R-value) of lateral system, provision of alternative load paths (to address progressive collapse), decoupling of lateral system from gravity system, system redundancies (e.g. use of full depth shear connections that can transmit diaphragm shear in addition to vertical shear), etc.
  • Structural Movement Joints: Are structural movement joints required? Where and how often are structural movement joints to be placed? Where are the lateral system frames located relative to these joints? For instance, locating lateral frames further away from the center of the diaphragm will increase member forces during an extreme temperature event.
  • Cladding Anchorage: How and where is the cladding anchored to structure? It’s generally best to apply any lateral forces directly to floor diaphragms. Does the superstructure support the weight of the cladding? How can cladding spans be configured to absorb the most energy and to minimize the forces transferred to the building frame during a disaster?

Once the risks have been determined and the building frame system has been chosen, the Structural Engineer must determine the required level of performance during a design event based on the client’s objectives, the acceptable amount of damage after one of these events, and the client’s budget. For example, ASCE 41 categorizes the performance of a structure during a seismic event in three levels: Immediate Occupancy, Life Safety and Collapse Prevention. Similar performance levels can be established and specifically tailored for different types of disasters. The goal is to determine how quickly after an event the building must be operational. In addition, the Structural Engineer must determine how, where and what level of ductility and redundancy must be provided to avoid a disproportionate level of damage or progressive collapse of the structure.

There are many ways Structural Engineers can be proactive about disaster preparedness, providing the best possible service to their client, serving their local community as well the overall engineering community. A Structural Engineer must effectively communicate with the design team and owner on what potential disasters must be considered, identifying what the code requirements are, and what the most efficient tools and methods for addressing those risks are. Structural Engineers can serve on code committees to advance current literature on addressing the risks posed by various disasters. It’s also important to be prepared for disasters by undergoing training on performing structural assessments of existing buildings post-disaster (e.g. ATC-20-1: Postearthquake Safety Evaluation of Buildings, ATC-45: Safety Evaluation of Buildings After Wind-Storms and Floods). Our ability to quickly assess the condition and level of damage of a structure after such an event is critical to the local government’s ability to assess the overall impact to a geographic area and the resources that will be required to reconstruct or remediate the area, as appropriate.

Structural Engineers play a critical role in impacting the disaster resilience of new and existing buildings and it is incumbent on all of us to be mindful of these risk factors in our day to day work. As climate change, sea level rise, and the frequency of extreme weather events continues to escalate, our ability to address these risks on a variety of fronts will be critical to the long term sustainability of our communities.
Read more...
 
SEI Sustainability Committee © 2011 DheTemplate.com & Main Blogger. Supported by Makeityourring Diamond Engagement Rings

You can add link or short description here