News and Events - "Technical Papers Library"

Welcome to our newsroom! Here you will find the latest information about our company, projects and people. Browse articles published by our engineers and scientists in national publications and conference proceedings, view our press releases and read through news coverage of Terracon.

If you are a member of the media, you may contact our media relations representative at media@terracon.com.


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Structural Steel and Welding Inspection – A Critical Service for Building Construction

FAA tower with rainbowStructural steel and welding inspection is a critical service for building construction. Poor welding or misalignment of steel components can adversely affect the structural performance or safety of a building. This is important for all buildings, but especially for critical structures such as hospitals and schools that must be able to withstand seismic events.

To protect buildings and their occupants, Terracon’s approach on structural steel projects is to form a close working partnership between our project inspectors and structural engineers.

Communication Yields the Best Results

Communication on these complex projects is key. Pre-fabrication and pre-erection meetings should be mandated to be sure that all team members (general contractor, inspector, fabricator, erector, and structural engineer) understand the requirements. These meetings are a good opportunity for the structural engineer to review the important aspects of the structural steel design, such as critical components like brace frames and moment frames.  Opening communication between inspectors and structural engineers saves time, allowing the inspector to help clarify project requirements, when questions come up during construction.

Welding procedures, applicable to the project, must be submitted and approved by the structural engineer.  Many structural engineers do not have the expertise to review welding procedures, and will utilize other consultants to advise and recommend acceptance.  Terracon has in-house welding experts to perform this welding procedure review.

Details are Critical

It is very important that structural components such as brace frames, moment frames, and other elements are installed in the proper location, within specified tolerances.  For upgrades in existing structures, there can often be existing conditions that interfere with the placement of the new structural steel members.

Inspectors must carefully detail any fit-up issues in the inspection report. The inspector needs to make sure that the contractor accurately describes nonconforming issues in Requests For Information (RFI) forms and submits them to the structural engineer for clarification and/or approved fixes.  Inspectors are required to be certified by the American Welding Society and/or the International Code Counsel and also need to be certified to perform, when required, nondestructive testing, such as ultrasonic or magnetic particle testing on welds.  These certifications require a high level of training and expertise.

A welding inspector must measure the size and length of every structural weld.  Field welds on brace frames are critical.  These welds are often welded out of position or can be undersized if there is a gap between the tube and gusset plate.  The fillet weld size must be increased by the size of the gap.  The alignment tolerances of the brace frame tubes are also critical and are usually detailed on the structural drawings.  There is often an erection bolt through the tube and gusset plate.  If the erector can’t get the erection bolt through the hole, there is likely an alignment issue that requires an RFI.

When welding new structural steel to existing structural steel, the existing steel must be cleaned to bare steel prior to welding.  Welding through coatings such as paint and galvanizing can lead to weld cracking and lack of weld fusion.

Bringing it All Together

When structural steel inspection is a required part of the project, it is important to build a collaborative team.  Structural steel and welding inspectors must have a high level of expertise and good communication skills. At Terracon, our materials professionals add value to your project at any stage. By joining your team early in the design process, we can identify, evaluate and recommend the right materials selection, welding procedures, and nondestructive testing, optimizing them for the project, which can speed construction and reduce costs.


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What’s Under the Hood (Concrete)?

Using ultrasonic echo tomography is a very useful structural diagnostic technique for diagnosing surface and internal concrete defects.

Ultra Sonic Echo TestingCracks, spalls, and surface defects such as voids, honeycombing, exposed rebar, etc., are typical symptoms of distress associated with reinforced concrete structures. These symptoms are typically identified as a precursor to a potentially larger issue hiding under the concrete surface. To an owner, this can mean unanticipated costs, potential impacts to building operations, and even safety concerns. The process of finding what has caused the defects will include an evaluation of distress symptoms such as cracks, voids, and surface defects. This effort requires a combination of visual assessment, and field and lab testing to develop a prognosis of the issue. One very useful and powerful tool used for assessment is ultrasonic echo tomography.

Defects in new or existing construction come from improper construction practices, improper design details, accidents, or sometimes natural disasters. These defects can impact the integrity of the structure and lead to sustainability and usability issues.

What is Ultrasonic Echo Tomography?

Ultrasonic echo tomography is a non-destructive test method used for evaluating the condition of hardened concrete by measuring the time of ultrasonic shear-wave transmitting in the hardened concrete. A shear-wave which is transmitted in an isotropic medium will be partly reflected when it reaches another medium with a different acoustic impedance. The amount of energy reflected depends on the significance of difference in the acoustic impedance of the two media. The effectiveness of ultrasonic echo testing in identifying defects inside concrete has been proven in many field applications.

3-D Ultra Sonic Testing

Diagnosis of A Reinforced Concrete Aeration Tank

This project involved a newly constructed cylindrical aeration tank that was designed to hold wastewater. The tank had an inner diameter of 63 feet, and a height of 18 feet. Our client observed concrete construction defects, including map pattern cracking, cold joints, and honeycombing on the exterior face of the reinforced 1-foot thick concrete wall of the tank after the forms were removed. These defects raised serious concerns related to the water-tightness of the concrete structure and its structural integrity.

Ultra Sonic Testing

To identify the probable causes of the observed defects, and determine if subsurface defects existed that were not visible on the surface, Terracon performed Ground Penetrating Radar (GPR) test and ultrasonic echo tomography test on the wall (on both interior and exterior faces) at several locations. The results of GPR test indicated inconsistent and less than specified concrete cover thickness near the exterior face of the wall which had contributed to the map pattern cracking mimicking the pattern of the reinforcing steel cage. Based on the 3-D models obtained from ultrasonic echo tomography test, the defects appeared to be limited to the vicinity of the exterior surface of wall, with no additional subsurface concrete flaws.  This was verified by through-wall coring performed on the concrete wall.

The findings allowed the client to determine that the new tank structure did not require demolition. They could be confident that the extent of observed surface defects were limited in nature. The structural engineer of record proposed a surface sealing repair coating to verify the water tightness of the structure. Significant demolition cost and schedule impacts were avoided.

Ultrasonic echo tomography is just one of the non-destructive techniques that can be utilized in evaluating concrete structures. With each unique project, a combination of a reasonable structural/materials evaluation and use of appropriate advanced non-destructive testing technology can help save time and money for all stakeholders.


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Beyond Drilling: Using Geophysics to Understand What's Beneath the Surface

ERI Foot SpacingDrilling and soil sampling has traditionally been the way to explore subsurface conditions. But what if your project site encompasses 18 acres and you know that highly variable conditions exist? Consider a site where drilling and sampling alone can’t sufficiently characterize the site.

Terracon’s regional geophysicists collaborate with our engineers and geologists to design the optimal geophysical survey to meet the client’s budget and needs. Terracon has an arsenal of geophysical tools and methods to supplement and complement these more traditional site characterization methods. Electrical Resistivity Imaging (ERI), is one such geophysical method and is a great tool for locations where drilling and sampling alone can’t get the job done. ERI measures relative average electrical resistivity of subsurface materials—or how strongly a given material opposes the flow of electric current—then processes the values into a 2-D cross-section of the subsurface beneath the survey line.

Geophysical methods such as ERI allow the identification of conditions underneath an entire area, as opposed to drilling and sampling soil borings which provide a finite extent of subgrade data at discrete locations. Using ERI as the first step in geotechnical site characterization is a perfect way to develop a smart exploration plan whereby borings and other intrusive sampling methods can be focused in critical or high interest areas identified by the ERI.

Starting an exploration program with ERI data may actually allow the reduction in the overall number of soil borings while painting a more thorough picture of the subsurface when complex geological conditions exist. Terracon’s team of geophysicists work with our geotechnical engineers to blend the use of geophysics with traditional drilling and sampling to better understand the subsurface in ways that have historically been impossible.

ERI In Action

Sometimes it’s not just geology that can create a complex subsurface that requires geophysics to understand. A client recently asked Terracon for help determining the condition of an area which formerly housed multiple coal mines.

Because our client planned to develop the site for commercial use, determining the extent and condition of the mines was essential to plan for future development. The existence of a non-operational coal mine could cause settlement and other foundation issues.

Our team started the exploration process with ERI, which provided data to predict the presence of the mine areas to approximately 120 feet below the surface. Our geophysicists evaluated the data and delineated certain areas and depths as anomalies potentially associated with previous mining operations. The geophysical survey allowed us to determine intact and collapsed areas, and areas with voids. We were able to hand this prediction of mine locations to our geotechnical engineers to perform an intrusive exploration with traditional soil borings to supplement and confirm the ERI results.

ERI measures relative average resistivity of subsurface materials—how strongly a given material opposes the flow of electric current—then processes the values into a 2-D cross-section of the area surveyed. ERI is usually performed in conjunction with or prior to drilling. It narrows down areas in need of further exploration to prevent “drilling blind.”

Revealing What Lies Beneath

This example is just one way that ERI can be used to reveal the subsurface conditions. We also recently used ERI to determine depth to bedrock below a guide wall at a lock and dam; identify karst (cave) features around a wind turbine farm; and locate water infiltration zones along levees. We even discovered a former tunnel near a clock tower.

Terracon has experienced geophysicists and the capability to execute numerous geophysical methods for site characterization throughout the entire country. In addition, NORCAL Geophysical Consultants, Inc. a Terracon Company, based in California, recently joined the firm greatly increasing our expertise in that region. The use of geophysics for subsurface characterization for geotechnical and environmental applications is rapidly growing. We continue to expand our knowledge of advanced geophysical methods such as ERI to bring reliable, cost-effective solutions to address the unique challenges of each site or project.


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Silica Exposure Limits: Changing the Way You Work

Silica is one of the most common, naturally-occurring elements on the planet. It is everywhere and, unfortunately, also known to present serious health hazards to people, especially those working in and around construction sites. The Occupational Safety and Health Administration (OSHA) has passed a new silica exposure rule which takes effect June 23, 2016. Companies have one year to meet compliance guidelines, and if you are in the construction industry, this rule will probably change the way you work. Full Story


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Selecting the Construction Materials Consultant with the Systems That are Right for Your Project Needs

At Terracon, we are continually looking for opportunities to provide more value to our clients and improve the way we do business. Hiring and training qualified people to work in construction materials is the most important investment we can make. In addition to having the right people in place, companies must invest in innovative systems that help deliver critical information to clients with speed and efficiency. Terracon’s Seamless Service Delivery approach gives us the ability to do just that. Full Story

 


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Air Barrier Testing Reveals Cost Reduction Solutions for School System

DSCN5239Ever notice a breeze in older buildings, even when it is not windy? Many buildings are leaking air, which means the owners are losing money. The Charlotte Mecklenburg School System (CMSS), one of the largest in the United States with a $1.3 billion operating budget, decided to take action to identify buildings in the school system that might be exhibiting air leakage. Full Story


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Just Testing or Real Teaming

The article discusses how advances in construction materials engineering testing and using advanced collaboration methods, can help achieve better results.


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Elevated Engineering

Roof top pools and other similar elevated swimming pool structures present a very unique set of considerations that must be thoroughly incorporated in the design and construction of these features. It is common that these elevated pools are constructed inside a concrete vault or on top of a concrete slab. The two-part article discusses the very unique structural loads exerted on these structures and the need to substantially increase the rebar schedules used in construction. The article also discusses the importance of waterproofing the interior of the concrete vault, and installation of a comprehensive drainage system between the vault and the shotcrete swimming pool structure. Several case histories are be presented as examples.  Full Article


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Gridiron Materials Testing: Preparing for Kickoff

Walter KrahlThe Minnesota Vikings have a new fan. Walter Krahl might not be sitting in one of U.S. Bank Stadium’s 65,400 seats next year when the NFL team hosts its season opener, but this Terracon materials inspector has been thinking about the Minnesota Vikings 2016 kickoff every day for more than two years.

Walter worked closely with the stadium’s owner representative, Hammes Company Sports Development Inc., providing structural steel inspections and testing at Alberici’s steel fabrication facility in St. Louis, Hillsdale Fabricators. This specialty fabrication shop, subcontracted by LeJeune Steel Company, created the heavy shape components (AISC) including the massive ridge truss, supporting columns and the thrust blocks installed as part of the stadium foundation system and entrenched in concrete to support the ridge truss. Full Story


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Here’s how to improve environmental health and safety

Don’t blame an employee for an unsafe behavior; instead look at the factors behind the act.

Proactive organizations recognize that adopting a “systems approach” to their environmental, health and safety (EHS) management creates a stronger, more sustainable platform for success. Full Story