Significant cracks on the exterior of a new building attract attention. When cracks recur after repeated attempts at repair, patience can be tested; once-good relationships among the owner, designer, and contractor may fray and monetary damages can be alleged. This article describes such a project and the unusual cause of the cracking.
A worship room addition to a church in the upper Midwest was completed in 2001. The addition was a one-story structure measuring 32 feet high with exterior walls clad in brick masonry. Sixteen fenestration openings, each measuring 12 feet high by 4-1/2 feet wide, were present along the east and west elevation exterior walls. The openings typically contained recessed and sloped insulated glass units (IGUs). Brick masonry-clad piers were present between adjacent openings, spaced at 5-1/2 feet on center. Each pier measured 12 feet tall by 1 foot wide, with a depth that varied from 12 to 18 inches over the height of the sloped glazing. (See Figure 1) No openings were present in the brick veneer above the 12-foot elevation, although vertical expansion joints were provided at regular spacing.
Hollow structural section (HSS) columns were provided at 11 feet on center, encased within every other brick pier at the east and west walls. No ties or mechanical connections were provided between the HSS columns and the brick pier cladding. The columns extended from the foundation walls to roof level. Wide-flange steel beams spanned between adjacent columns across the top of the fenestration openings. The beams supported the brick backup wall, consisting of concrete masonry, which extended to roof level. Steel plates were welded to the beam bottom flanges to serve as lintels that supported the brick veneer above the 12 foot elevation.
The brick veneer was completed in the summer of 2000 and cracks were noted in several piers by December. Despite a variety of attempted repairs, the cracking issues recurred almost annually over the next eight years. The cracks were consistently located in only the bottom half of the piers, and were predominantly vertical. The cracks most frequently formed in the winter seasons and on the outboard faces of the piers, particularly those with underlying HSS columns. (Figure 2 on opposite page)
Various investigations and analyses of the cracking issues were performed between 2001 and 2007 by the original structural designer, the general contractor, and an independent structural engineer, among others. Theories and allegations abounded, including both design- and construction-related issues, although the cracking was most commonly attributed to compressive failure of the masonry. Many of the assertions prompted new repair strategies, or modifications to the as-built construction, or both. At least a few of the piers were entirely re-clad. And yet, the cracking continued.
Wiss, Janney, Elstner Associates, Inc. was retained in 2008 to investigate the cause of the pier cracking. The investigation consisted of: 1) reviewing all available background information, project documents, design and shop drawings and reports; 2) inspecting and documenting interior and exterior conditions; 3) observing conditions at four destructive inspection openings created into the pier cladding; and 4) performing structural analyses.
Exterior observations identified cracks in several brick piers on both the west and east sides of the addition. The cracks typically extended from just above grade to the approximate mid-height of the piers. The crack widths varied from 1/32 to 7/16 inches, with the underlying HSS column visible through one of the wider cracks. Interior observations revealed no visible evidence of water leakage and no significant finish distress or other evidence of movement at the piers. Structural analyses confirmed that the HSS columns, steel beams and lintel plates possessed sufficient capacity for the design loads. Calculations were also performed to estimate the compressive stresses in the pier cladding associated with the combined effects of self-weight and restrained temperature and moisture-related expansion. The analyses indicated that no cracking of the masonry would be expected as a result of these considerations.
Exterior inspection openings were created at the top and bottom of select piers that exhibited the cracking conditions. The objective was to inspect and document the as-built construction. At the top of piers, movement joints were partially occluded with mortar and through-wall flashing defects were present. At the bottom of the piers, the space between the brick and HSS columns was less than 1/2 inch wide and it was fully congested with mortar droppings.
The inspection openings at the base of the cracked piers exposed the sides of the HSS columns. At both locations, the column sidewalls appeared to exhibit outward bulging, with amplitudes of up to approximately 5/16 inch. (Figure 3 above) No weld cracking or other obvious column distress was observed.
A 1/4-inch-diameter hole was drilled through the bulged sidewall of the HSS columns at both of the lower inspection opening locations. Water immediately sprayed from the hole at a high velocity. (Figure 4 above) Water drained from one column for 10 minutes, and for 30 minutes from another. Based upon the volume and flow rate of the water coming from the drilled holes, engineers estimated the depth of water within the two HSS columns to be no less than five feet.
The principal cause of the cracking in the brick piers was determined to be water trapped within the HSS columns from the time of the original construction. The freezing and expanding of this water resulted in outward bulging of the column sidewalls. Because mortar droppings filled the space between the pier cladding and the sidewalls, the bulging of the column sidewalls caused lateral loading of the brick masonry on the sides of the piers. Vertical cracks developed in the pier cladding in response to the sidewall distortion. A review of the structural steel shop drawings confirmed that the trapped water was not the result of water infiltration after construction.
The possibility of water becoming trapped within HSS shapes is recognized in AISC 360 – Specification for Structural Steel Buildings. Specifically, AISC 360 states, "When water can collect inside HSS or box members, either during construction or during service, the member shall be sealed, provided with a drain hole at the base, or protected by other suitable means." It further states that "Care should be taken to ensure that water does not remain in the HSS during or after construction, since the expansion caused by freezing can create pressure that is sufficient to burst an HSS."
In addition, for the 1983 ASCE Conference, James Cran, MSCE, FEIC, authored an article titled "HSS – The Questions of Icing & Internal Corrosion." This article discussed case studies where the freezing of trapped water caused bulging and fracturing of HSS members.
This project illustrates an example of the costly, yet completely avoidable, issues that can ensue when the precautions outlined by AISC 360 – Specification for Structural Steel Buildings are not followed. When investigating distress conditions, keep an open mind to all potential causes. The usual suspects are always worthy of evaluation but the unlikely culprits are not always unlikely.
Brian J. Pashina, P.E., is a principal and Mark R. Chauvin, P.E., is an associate principal at Wiss, Janney, Elstner Associates, Inc. in Minneapolis, Minn. Contact Pashina at BPashina@wje.com and Chauvin at MChauvin@wje.com.