Planning to Succeed: Bracing and Shoring

Maintain balance, dynamic stability, and structural integrity of individual building elements.

Failing to Plan or Planning to Succeed?

MANAGEMENT By Michael Walsh

Dealing with the physical realities of temporary or partially completed structures

Michael Walsh is President of Dearborn Engineers & Constructors, Inc., Bridgeview, Illinois, a leading consultancy specializing in heavy lift, heavy transport and construction-erection engineering on a national basis. Contact him at MWalsh@DearbornCos.com. installed elements need protection from overstress and potential damage. Beyond simply making sure that the structure stands-up, the construction also needs to move forward safely, efficiently and cost effectively.

Benjamin Franklin famously coined the phrase, “If you fail to plan, you are planning to fail,” which is an adage that is highly applicable in construction, with compressed schedules and strained supply chains. Practical solutions to complex problems demand speed and collaboration, particularly for those like steel erectors, who are at the “tip of the spear” on a project. Timely planning is critical, and erection engineering is critical to planning.

Project design teams work in a virtual world where individual building elements are treated and function as completed systems. Steel erectors, however, deal with the physical realities that accompany temporary and partially completed structures, until that completed design stage is achieved.

Regardless of the stage of construction, erectors are required to maintain structural stability and integrity, while being resistant to temporary and transient loads that may exceed those of the final design. Permanently installed elements need protection from overstress and potential damage. Beyond simply making sure that the structure stands-up, the construction also needs to move forward safely, efficiently and cost effectively.

Key in making all of this happen is the early involvement of an experienced erection engineer (EE) in the planning process.

Codes, Standards, Design Intent

At the start, a practiced EE will be able to assist you in utilizing the correct code or industry standard, which can dramatically impact the safe, successful, and timely completion of your project. Nuanced differences in design values and safety factors among AISC 303, ASCE 37, SJI, and/or PCI standards can have significant effects on sequencing and costs of bracing, shoring, and temporary supports.

Personal experience has shown ASCE 37 to be a bit more reflective of actual encountered loads, which can offer some benefits in terms of sizing and positioning of bracing and supports, but each project must be evaluated on a case-by-case basis. It is very important to remember that codes and standards provide the minimum criteria to be met and often do not rise to the level of what’s deemed “good” (not “best,” but good) engineering or industry practice.

Development of a clear understanding of the “Engineer of Record’s” (EOR’s) intended performance of the completed structure is critical, and your EE will provide insights to help avoid the potential for overload conditions. All loads – live, dead, construction (including material staging, tools, and equipment), shoring and bracing, safety related, and even surcharges and earth pressure loads – require consideration. Understanding the completed structure’s performance will identify where temporary erection loads can be dragged and offer you real guidance in where to physically start the erection process.

Sequencing the Work

Steel erection is, by its nature, an iterative process. Sequencing of the work requires maintaining a balance between structural stability and the ability to physically access building elements and efficiently perform the work. As an example, the choice between first starting a building with its exterior precast concrete shear walls versus starting with its structural steel frame can have a profound impact on the sequencing and temporary supports for both erection processes.

Inherent in this iterative process is the fact that during erection the permanent structural system is not complete and may require the engineering design of connections and temporary members possessing far greater capacity than those of the permanent structure. Open structures are subject to lateral and uplift wind loads that the permanently closed structure will not experience, nor was designed for. The imposition of these loads, if not properly accommodated, can cause single-point or localized damage, or in the extreme, the progressive collapse of the entire structure.

Thinking the “Unthinkable”

Another adage applicable to construction is, “Murphy was an optimist.” The need to look beyond the obvious and work to anticipate potential “unforeseen” failures is essential. While an episode like the Hard Rock Hotel collapse in New Orleans is an extreme example, erectors and their EEs need to push the envelope in evaluating temporary construction vulnerabilities to ensure the safe and successful completion of projects.

Coastal areas that are subject to severe storms and tidal activities, northern areas subject to heavy snows and severe cold, and seismically active areas, all require special design considerations in protecting both temporary and permanent construction.

• monitoring and reporting measures for extreme environmental conditions;

• defined provisions for protecting construction personnel and the general public (up to and including evacuation plans); and

• detailed protection of adjacent structures and facilities.

In addition to environmental factors, other potential safety and stability threats require evaluation and accommodation. Potential shock loads imposed by worker fall protection systems or debris nets, dropped material impact loads, tool and material staging dead loads, manlift and mini-crane dynamic loads, even personnel live loads, need consideration.

Also requiring very close consideration is protection against the accidental or unplanned removal of temporary supports, shoring and bracing, followed with detailed procedures for its planned removal upon completion of the associated work.

Beyond the Box

Compounding the variables directly at play in safe erection of the structure, are a multitude of other considerations to be taken into account. Balance, dynamic stability, and the structural integrity of individual building elements (particularly those with long-spans), require special attention for safe hoisting and setting. Unaccounted for deflection during hoisting operations can lead to excessive deformation and potential failure of the member. Excessive loading during placement can result in overstressing of anchors, base plates, and foundations.

Rigging elements (slings, chokers, spreader bars, and other hardware) also require proper evaluation and selection. The location and positioning of cranes and derricks to optimize hoisting operations needs to be coordinated with other ongoing construction activities, such as excavation and concrete placement. Site ground conditions require assessment in terms of soil stability in advance of the deployment and operation of hoisting equipment and aerial lifts, and for the placement of shoring and bracing.

Planning for Success

We live and work in a highly dynamic environment, subject to an incredible number of variables. While some may perceive the EE simply as “added cost” to a project, the early involvement of a knowledgeable, experienced engineer, possessing good communications skills, can genuinely make the entire construction process smoother, easier, and significantly safer. •