Structural, Architectural, &
When the forces applied to a structure exceed the structure’s capacity, a failure will occur. Structural failures are often caused by natural perils, design and construction deficiencies, deferred maintenance, and misuse. Nelson’s structural, architectural, and civil engineers specialize in assessing the cause and extent of damage and defects to many types of structural systems; including buildings, bridges, towers, tanks, racks, retaining walls, pavements, and components thereof. These professionals also develop solutions to remediate, repair, and strengthen damaged and defective structural systems.
Nelson’s engineers are experts at investigating failures due to hurricanes, tornadoes, storms, floods, fires, vibrations, impacts, explosions, earthquakes, unstable soils, and material defects.
They also assess the effects of design defects, construction defects, and improper use on the strength, serviceability, and durability of structures. Nelson’s engineers are experienced in evaluating commercial, industrial, residential, institutional, educational, healthcare, athletic, marine, infrastructure and agricultural structures, among others.
The roof of a two-story office building collapsed during a severe rainstorm. The impact from the collapsing roof progressively caused the second floor to also collapse onto the first floor slab. Nelson documented the collapse and analyzed the framing system and the roof drainage, and ultimately determined that the failure was the result of clogged primary and secondary roof drains, in combination with rainfall which exceeded the 100 year design storm for the area.
This case involved a building which had been recently converted from a gas station into a café. A 2 inch rainfall occurred shortly after the conversion was completed, and caused a catastrophic failure of the wood-framed roof system while the café was occupied. Nelson documented the collapse scene, retained evidence, reviewed the original and retrofit construction documents, and performed rigorous structural and roof drainage analyses. Nelson’s engineers determined that the roof collapsed under a very light rain load because a larger air-conditioning unit had been placed atop the roof as part of the conversion to a food service facility. Structural upgrades were not performed to support the new air conditioning unit, and it overstressed the roof system. In this case, the rain was the “straw that broke the camel’s back.”
A highway bridge collapsed while in service. The bridge was a 1940’s era reinforced concrete multi-arch superstructure supported by wide-flange steel columns. Nelson’s engineers documented the collapse and the structural elements of the bridge and analyzed the structural response to the heavy loads which were in place at the time of the collapse. Nelson determined that the bridge collapsed due to a vehicle load in excess of the rated capacity of the bridge, in concert with severe deterioration of the steel substructure.
The roof at a water park facility attached to a resort collapsed overnight under negligible environmental loads, and after ten years of service. The structure had been in use the previous day. Roof framing at the waterpark consisted of double (i.e., 2-ply) metal plate connected (MPC) wood scissor trusses, each 90 feet in length, with a corresponding single MPC piggyback truss (a.k.a., cap truss). The roof framing was supported by 18-foot tall bearing walls, which were framed with engineered wood studs. Nelson’s investigation determined the collapse was the result of inadequate installation of the required permanent lateral bracing system, and not the result of design deficiencies related to the individual truss components.
Fertilizer Plant Explosion
On April 17, 2013, an explosion at the West Fertilizer Company in West, Texas rocked the city and surrounding rural areas. The explosion left a crater 93′ wide and 10′ deep, caused 15 fatalities, and over 200 injuries. As a result of the extensive damage caused by the explosion, Nelson’s professionals evaluated numerous buildings throughout the city.
Nelson’s team published Performance of Structures Subjected to West Fertilizer Company Explosion in the proceedings of the 2015 American Society of Civil Engineers Forensics Congress. The publication presented a study of the respective performance of the evaluated buildings subjected to the explosion, particularly in relation to the distance from the explosion’s origin, and revealed solid correlations between published damage indicator data to the observed damage.
Nelson’s rapid-response teams have evaluated hundreds of buildings following tornado events nationwide. Often working alongside emergency response personnel, Nelson’s engineers have assessed the safety of affected buildings, determined the extent of damage caused by tornadoes, and compared the same to code requirements for structural strength and stability. Nelson’s engineers have recommended remediation for some affected buildings, and suggested demolition of others which were damaged beyond the limits of economical repair.
Nelson personnel responded immediately to the sites of EF-5 tornado damage in Joplin, Missouri and Moore, Oklahoma. Nelson’s engineers also assisted in damage evaluations following the Vilonia, Arkansas EF-5 tornado; the 2014 84-tornado outbreak; and the 2011 Super Outbreak, where 360 tornadoes touched down in 21 states.
While roof collapses are not uncommon, this case was unique, as the steel joist roof framing collapsed along the entire 900 foot length of one perimeter wall. Nelson’s engineers responded immediately, documented the collapse, and analyzed the evidence to determine the cause of the failure. The failure mode was determined to be related to deficiencies in the design and manufacturing of the welds connecting the joist members, and then subsequent tearing of the steel material around the welded connections. The joists utilized in this structure were a new product to the market, and testing of the joists revealed that they were prone to this type of sudden failure.
Within a few years of completion of this post-tensioned concrete parking garage, multiple failures of the tendons occurred, compromising the structural integrity of the garage. Nelson performed a structural evaluation of the garage, monitored the condition of the garage over time, and communicated with the original design professionals. Nelson created testing protocols and developed a testing program for the garage, including exposure of tendon anchorages and removal and replacement of a portion of the tendons. Nelson further coordinated metallurgical testing of the tendons and petrographic testing of the grout and surfacing materials. Ultimately, the cause of the failures was determined to be accelerated corrosion caused by installation deficiencies, including poorly consolidated grout pockets at the tendon ends. After identifying the cause of the failures, Nelson’s engineers assisted with developing a remediation protocol to repair the garage.
On August 29, 2005, Hurricane Katrina ravaged the city of New Orleans, causing wind damage and major flooding. Nelson evaluated flood damage to scores of residential buildings affected by the historic levee breach to determine whether they met the commonality requirements for class certification.
Nelson’s teams also analyzed dozens of buildings at a major university in New Orleans. Site investigations included assessment of roofing, exterior/facade, interior, structural framing, foundation, electrical systems and equipment, and mechanical systems and equipment. Subject buildings included single- and multi-story administrative offices, classrooms, libraries, dormitories, athletic facilities, historical structures, and physical plants.
Dallas Cowboys Practice Facility
The 83,000 square foot steel-framed membrane-envelope building housed a full-size football field and observation areas; and it collapsed during a windstorm with maximum wind speeds of 55 mph. Nelson’s team of engineers responded immediately to document the collapse scene, collect evidence, and ultimately determine the cause of the failure. Nelson’s team directed the controlled dismantling of the remnants of the facility and transportation of the evidence to a secure storage facility. Nelson’s forensic analysts performed load development based on forensic meteorological data, wind/structure interaction analysis, and extensive finite-element modeling of the global structural system and solids continuum modeling of structural connections. The numerical modeling results were validated with physical evidence, and the cause of the collapse was determined to be related to deficient structural design.
A two-span pedestrian bridge which connected the second floor of a shopping mall with the adjacent parking garage collapsed. The bridge was constructed of wide-flange steel fascia girders, transverse floor beams, and concrete on corrugated steel deck. Nelson documented and analyzed the collapsed bridge, and determined that the bridge failed under its own weight due to severe long-term deterioration of the steel support framing.
Allen Eagle Stadium
Two years after construction of the $60,000,000, 18,000 seat Eagle Stadium in Allen, Texas was completed, Nelson was retained to evaluate unusual cracking at the elevated, reinforced concrete concourse level. Upon initial review of the structural plans, Nelson identified deficiencies in the concourse level framing, and subsequently recommended a full review of the as-built construction documents for the entire stadium. Nelson’s review uncovered flaws in many of the structural load carrying elements of the stadium. Those design flaws, in concert with construction deficiencies, rendered the stadium unsuitable for occupancy, and necessitated a massive repair and strengthening effort. Nelson participated in design of the repair and strengthening solutions in close collaboration with structural design firm Datum Engineers, performed construction administration during the repair effort, and assisted with dispute resolution. The stadium reopened 14 months after its closing.
The 7 Line
The New York City 7 Subway Extension was a key part of the $2,000,000,000 Hudson Yards Redevelopment Project. The extension stretches from Times Square to a new station at 34th Street and Eleventh Avenue. Shortly after construction, water intrusion into the new subway tunnels and station was discovered, and Nelson was retained to determine the cause. Nelson evaluated the tunnels and station, and reviewed construction documents, quality control procedures, material properties, construction methods, reinforced concrete design, and building code requirements. Nelson’s engineers determined the causes of the water intrusion and provided solutions to the client to remedy the situation.