David B. Peraza

Engineering Considerations for Lift-Slab Construction

Sponsored by the Task Committee on Lift-Slab Construction of the Technical Council on Forensic Engineering of ASCE.

Condition Assessment of Buildings

There are many different types of structural condition assessments of buildings, depending on the circumstances and the objective of the client. The assessments can vary widely in terms of their scope, the level of detail and their comprehensiveness. However, some types of inspections are reoccurring. This paper presents the most common types of structural condition assessments that are performed on buildings or on portions of buildings. It includes the purposes of the assessments, common problems, methodologies, and strategies for performing a high quality assessment. The principles presented apply to all types of buildings, including steel construction, reinforced concrete, high-rises, and industrial facilities. As a case study, the application of these principles to the buildings surrounding the World Trade Center following the 9/11 attack are presented.

Estimating the Storm Surge Recurrence Interval for Hurricane Sandy

Hurricane Sandy’s storm surge peaked at 2.87 m (9.40 ft) above mean sea level (MSL) (9.64 ft Manhattan Borough Datum [MBD]) at the southern tip of Manhattan in New York City on October 29, 2012 at 9:24 pm. The peak storm surge coincided with a tide of 0.64 m MSL (0.24 ft MBD), only 30 minutes after a high tide, contributing to catastrophic flooding of near-coastal areas. Traditional flood analysis fitting techniques using various probability distribution functions (normal, lognormal, Gumbel, and log-Pierson III) yielded return frequencies from 667 years to over 10,000 years. The more advanced Lin et al. (2010; 2012) analyses yielded recurrence intervals of between 559 and 650 years for the storm surge alone and 993 years for the surge plus tide. Considering the 2.77-mm/yr (0.11-in/yr) sea-level rise and using the analysis of Lin et al. (2012), future storms equal in magnitude to Hurricane Sandy will result in even greater flooding.

Challenges in Renovation of Vintage Buildings

AbstractStructural engineers often encounter various unique design and construction challenges during renovations of vintage buildings. If such challenges are not properly addressed, they may result in major consequences. This paper provides a case study of a flawed structural renovation project and discusses the common challenges that engineers may face during renovation projects. The subject building is a six-story vintage residential building with a structure consisting of exterior load-bearing brick masonry walls, interior cast iron and wood columns, and wood floor framing. The renovation project mainly included the addition of a penthouse, addition of a freestanding fireplace and chimney, and converting a roof into a roof garden for the owner of the top story of the building. Due to several serious structural issues that were discovered during and after the renovation project, the penthouse, fireplace, and chimney had to be demolished, and usage of parts of the apartment was restricted to prevent str...

Special Problems with Composite Multiwythe Masonry Walls

Composite multi-wythe walls for exterior walls, especially those that combine brick units and concrete masonry units (CMU), are vulnerable to certain special problems. There are a considerable number of existing structures that were built using this type of construction, and it is still occasionally used for new construction. These types of walls are prone to certain problems, and these problems are not generally well known among engineers and architects. The result is that existing buildings that show symptoms of these problems may be misdiagnosed, leading to inappropriate or expensive repairs, and that design professionals may not be fully aware of the pitfalls when they use this system for a new design. This paper discusses the vulnerabilities of this type of construction, surveys the available literature on the topic, and illustrates the issues with a case study

Snow-Related Roof Collapses—Several Case Studies

Heavy snowfall in the winters of 1993–94 and 1995–96 triggered numerous collapses in the northeastern part of the United States. This paper presents three case studies that were investigated by the writers firm. Topics covered for each case study include specific climatological. circumstances, comparison to code provisions, results of structural analyses, and lessons learned. In each case, it appears that the snow load on the roof exceeded the design value given in the governing building code, by a greater margin than might be expected from the amount of precipitation alone. Issues needing additional research are also identified, such as accumulation on cold roofs, effects of freezing and thawing cycles, snow drifting on large roofs, and the effectiveness of bracing provided by standing seam roofs.

Collapse of Crossed Pendulum Ceiling Systems Due to Unstable Equilibrium

A failure analysis was conducted following the collapse of a 13,000 lbs., 165 ft by 16 ft rectangular steel suspended ceiling panel structure in a large public space. The ceiling framing structure was suspended from the roof structure with a unique system of stainless steel cables that cross one another between the ceiling structure attachment points and the anchorage to the supporting slab above. During construction, the entire ceiling panel structure rotated out of its installed horizontal position when the temporary cable bracing was removed, causing one edge of the ceiling structure to drop suddenly and the opposite edge to lift. No failure of the suspension cables or their attachments occurred. The collapse was caused by a design error that did not properly consider the stability of the suspended ceiling panel. The behavior of this particular ceiling panel structure is generalized to a wider class of crossed pendulum structures, and stability conditions based purely on system geometry are found using energy principles for a wide set of feasible parameters. Guidance is provided for the design of suspended systems involving crossed hangers, such as ceiling structures, bridges, and suspended walkways.

BEST PRACTICES FOR CONDUCTING PRE-CONSTRUCTION SURVEYS: LESSONS LEARNED FROM CONSTRUCTION CLAIMS

Demolition, excavation, and construction that are performed in close proximity to existing buildings and structures, and in particular those in an urban environment, may cause damage to the surrounding structures ranging from the loss of serviceability to complete collapse. In these instances, disputes often arise over the cause and the extent of the damage and also the roles and responsibilities of the contractors engaged in the work. A forensic investigation of the alleged damage, and in particular, the cause and the extent of the damage and a determination of new versus pre-existing damage after the construction has begun, or after it has been completed, can be challenging. One approach is to compare the alleged damage with those conditions, or the lack of conditions, identified in the pre-construction survey report. This paper surveys the industry literature on the code requirements for conducting pre-construction surveys, practices for conducting condition surveys used in the assessment and the rehabilitation of existing structures, and types of damage and the causes of that damage that are often alleged in construction claims arising from adjacent construction. This paper also compiles some of the best practices for conducting pre-construction surveys and for reporting the findings. These practices are taken from the lessons learned from actual construction claim disputes.