Completed Strengthening Project – Two Storey Office

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35 Sir William Pickering Drive

Seismic Strengthening of office building

 

The Building

This is a two-story office building that consists of concrete and steel structures. The lateral system relies on the reinforced concrete, shear wall panels in both transverse and longitudinal directions. The building is being occupied by different businesses which operate Monday through Friday from 8am to 6pm. The office operating times are very important in relation to our strengthening scheme.

Strengthening Process

The owner of the building had engaged the original structural designer to provide a strengthening scheme, but it appears the solution didn’t work for the Owner. I’m assuming this had to do with the practicality and consideration of the building’s occupants. The owner had engaged another structural engineering consultant to provide an alternative solution, but again, the owner did not approve because the scheme also disrupted the current occupants’ everyday routines. On his third try, the owner approached us, asking us to review the current strengthening scheme, while simultaneously creating a way to minimize the disruption of the tenants.

The building has a typical L-shape floor plan which has a potential torsional issue. A number of shear walls are to be placed at several locations, resulting in the seismic loads being more distributed to the lateral components of the building.

We carried out an independent inspection and assessment of the building and followed that up with a Detailed Seismic Assessment (DSA) to verify the current structural condition of the building. We also carried out a structural analysis using a state-of-the-art structural analysis software. After thorough analysis and design, we came up with a new and improved strengthening scheme, which provides less space intrusiveness and lower construction costs.  Most of our seismic strengthening scheme occurs outside the building, meaning there is a minimal disruption to the occupants’ activities.

The strengthening scheme that has been undertaken will result in the building becoming more stable, while achieving at least 80% of the New Building Standard or 80%NBS.

Final Thoughts

Strengthening your building can be a headache, hassle, and an expensive exercise if not done well. The key factor to consider involves engaging the right people for the job. Those who will understand your requirements, constraints, and budget.

Please do not hesitate to give me a call to discuss your current project or to offer you some helpful advice.

Email: andre@istructures.co.nz, Mobile: +64 21 213 0698, Skype: andre.boiser

Strengthen Your Building or Pay the Price

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  • $3.8 billion per year to repair earthquake damage in Italy between 1968 to 2014
  • 10% of New Zealand GDP equivalent damage during the 2010-2011 earthquakes
  • $30 billion in Chile in 2010, $300 billion in Japan and $10 billion in Nepal 2015 earthquake.

Older buildings in New Zealand need to be strengthened before the next earthquake strikes or pay the price. Strengthening should not be an option, it must be mandatory for both the safety of users and reduced repair costs.

Earthquakes represent one of the most destructive natural hazards for many countries around the world, including New Zealand. For instance in Europe, although earthquakes represented only 5% of the recorded major events (natural hazards and technological accidents), in the period 1998-2009, they were responsible for about 20% of the total number of fatalities (18,864 people) and overall losses (29.2 billion euros)[1]. The cost of recent earthquakes is even larger for regions with higher seismicity. For example: Chile 2010 ($30 billion), Haiti 2010 ($14 billion – more than 100% of the country’s GDP), Christchurch 2010-2011 ($20 billion – 10% of country’s GDP), Tohoku, Japan 2011 ($300 billion associated with both earthquake and tsunami damages) and Nepal 2015 ($10 billion).

The benefit of #strengthening a structure before the earthquake strikes is usually demonstrated through a strengthening cost-benefit analysis of buildings that have damaged by an earthquake. The results of such a study are shown in Table 1. It can be seen that the cost of repairing high-risk building (structural and non-structural) is four times higher compared to the buildings with limited structural damage. It also showed that the cost of strengthening is more than double.

Database of RC buildings

According to a report published by the Center of Studies of the National Council of Engineers of Italy entitled “Costs of earthquakes in Italy”, in total between 1968 and 2014 121.6 billion euros were spent for reconstructions (Fig. 1). This is equivalent to spending 2.6 billion euros per year to repair the damages caused by earthquakes. According to one of the general directors of the Civil Protection Department, Mauro Dolce, about 50 billion euros would be needed to render all public buildings earthquake-resistant. The estimation of the necessary cost for the strengthening of all private structures is not so easy since each owner can opt for a different strengthening strategy associated with costs varying from 300 to 800 euros per square meter. According to the Italian Civil Protection data, about 93.7 billion euros would be needed to provide safety of all Italian houses in the case of an earthquake, while structural interventions in zones with high seismic risk would cost approximately 36 billion euros. Considering that the reconstruction costs of 121.6 billion euros concerned only a small percentage of the Italian building stock that was exposed to earthquakes during the period 1968-2014, spending 144 billion euros for strengthening all buildings of the country is expected to be an affordable cost for a developed society to undertake on a long-term basis.

Reconstructions Costs

The need for seismic strengthening of structures before a strong ground shaking arrives can be illustrated by examining the seismic behavior of two identical Victorian style buildings in Santa Cruz, California during the 7.1 magnitude Loma Prieta earthquake in 1989 (http://www.earthquakesafety.com/retrofit-case-study.html). According to the owner and architect Michael O’Hearn, the twins were built 90 to 100 years ago, by the same builder, with identical materials and using the same construction techniques. He started building structural wood panels as a shear element on cripple wall framing for one of the twin buildings. The sill plate also was bolted to the foundation. Unfortunately, there was no time to install structural wood panels at the other building as well before the Loma Prieta earthquake. The non-strengthened building came apart in four sections and its five residents survived by luck. The repair cost was approximately $260,000 since the entire building had to be jacked up and slid back together on a new foundation. On the other hand, the building with the structural wood panel shear walls experienced only minor damage (repair costs of approximately $5,000). Although this cost difference might not be representative of all cases, it gives an idea about how important pre-seismic strengthening over post-seismic strengthening/repair is.

It should be also noted that all potential consequences must be considered when performing a cost-benefit analysis for the seismic strengthening of a structure, including the human dimension. The most objective way to estimate the cost of human life is insurance data. Earthquakes in developing countries, such as Haiti or Chile, might result in large amount of casualties and injuries, affecting the post-earthquake recovery, the reconstruction and also the Gross Domestic Product of the country. Moreover, since in developing countries life insurance and disaster insurance are rather uncommon, an earthquake strike can lead to poverty for a large part of the population (https://courses.edx.org/courses/course-v1:EPFLx+Tech4DRR+2016_T3/info). Developed countries (e.g. U.S.A., Japan, New Zealand, Italy) usually experience much lesser number of casualties compared to developing countries but since their GDP is based on the contribution of the tertiary sector (services, commerce, transport, tourism), damages in housing, infrastructures, and lifelines might lead to an important economic setback.

In the next few articles, I will outline the most common strengthening techniques applicable to different types of buildings.

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Recent investigation of the Ministry of Business and Innovation and employment (MBIE) have showed evidence of non-compliant sub-floor and foundation repairs in the Canterbury regions.

Examples are:
1. Patched up foundation crack repairs
2. Shoddy pile packing or jack & pack method
3. Floor level is outside tolerance
4. Walls are out of plumb
5. Undocumented repairs done, no engineer sign off, no council record

It is very important to verify if the repairs done to your home is up to standard, otherwise it will pose potential risk with your investment.

iStructures had been involved in the earthquake assessment since 2011, please do not hesitate to contact us if you want your subfloor or foundation check.

Please call 03 348 5755 or email at admin@istructures.co.nz

Danger in unreinforced chimney and its solutions

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With the ongoing earthquakes around New Zealand, it would be wise to look at the solutions of your old and unreinforced chimney before it gets damaged by the earthquake.

The cost savings is huge if we can address the potential issues at the early stage. Here’s the comparison;

Mitigation of Non-damaged chimney
1. Design fees and City council fees
2. Chimney construction cost

Repairing of earthquake damage chimneys
1. Temporary repair cost
2. Repair damage to roofing
3. Repair damage to ceiling and maybe flooring
4. Accommodation of the homeowner
5. Design fees and City Council fees
6. Chimney construction costs
7. Potentially the lower part of the chimney below ceiling is damaged as well, therefore it will add the cost of the construction.

Since 2011, iStructures NZ Ltd is helping the Earthquake Commission through EQR in providing latest chimney design to mitigate the potential damage in future earthquakes.

iStructures will carry out inspection of your old chimneys, develop design, manage the process and manage the construction.

Decide today!

Contact us by email at admin@istructures .co.nz or phone us +03 3485755

iStructures can help in architectural design, structural design, building consent process, construction management and building works.

www.istructures.co.nz

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Structural Design: Innovation – Collaboration – Easy 

By iStructures Structural Team Leader, Hendry Sutjiadi

Structural engineering is one of the specialties of iStructures. As a team, we implement the company’s motto: Innovation-Collaboration-Easy in all we do. This is not merely a slogan, but it is a powerful tool to ensure iStructures’ structural design and engineering solutions are of the highest standard.

An example project that we have successfully applied the motto to is the structural design of a series of 3-storey dwelling units. It consists of 4 apartment blocks with each having a unique architectural building shape. The buildings stand on TC2 land in Linwood.

To answer the challenge of the design process, we had to be innovative. We applied light-weight steel framing as the main structural system of the buildings. The main purpose was to reduce the building self-weight and seismic load. As a result, the foundations could be more effective compared to those that use traditional steel or reinforced concrete structures.

In developing the structural design, we carried out 3D modelling of the light-gage steel structures. We used aArchitectural modeln integrated software package that enabled us to do structural design, CAD drafting and detailing in a single package. One of the buildings had a large open space at the ground floor for the carpark, which was another design challenge. A hot-rolled steel structure was used to support the upper floor’s light-gage structure. An innovative design methodology applied a combination of two separate 3D modelling program. The upper and lower structures were then analyzed separately.

Another challenge of the structural design was the complex roof shapes. The architectural team, which is part of iStructures, had designed the building with an elegant roof to maintain a high architectural standard. The ceiling of the top floor was designed to correspond with the stylish roof shape. Close collaboration with the architectural team was the key to ensure a successful project outcome.

3d modelLast but not least is to make all jobs easy. This means that no job is too complicated if we can be innovative and collaborative. Excellent communication within the team and with the other teams in the company is the key to ensure that a high degree of innovation and collaboration is taking place and making the job easy. This also applies to external parties, such as our clients, contractors and the councils. Our customers are very satisfied with iStructures because we are easy to deal with, providing solutions beyond their expectations.

iStructures, Innovation-Collaboration-Easy has successfully been applied to our projects with the company continuing to make a strong contribution in rebuilding Christchurch. For more information on iStructures, phone 03 348 5752 or visit our website www.istructures.co.nz.

48 Barbour

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iStructure’s project in 48 Barbour is nearly finished.  Interior and Exterior painting works has been done during the holidays.  The homeowner’s choices of color are simple and elegant, complementing the house design.  iStructures Ltd always ensures  that homeowners are happy with the results.20160111_153608 20160111_153734 20160111_153912

Nik Buffham, Project Manager

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I write to thank you for your expert service to our company.
Your staff are always friendly and efficient in their site visits helping us to put homeowners at ease in the earthquake repair process. The technical reports we receive are concise and detailed providing ample information to proceed with repairs with confidence.
Our customers often comment on the high quality of reports we receive from you.
Lighting Construction and Joinery look forward to a long and mutually beneficial relationship with iStructures.

consulting-engineers

Mark Parry, Project Engineer

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iStructures provided us with top-quality mechanical drawings at a very reasonable price. Their highly professional and efficient service was of immense benefit to our business, enabling us to spend more time getting the job done.