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Replacing Joists at Office/Warehouse and Distribution Buildings

Written by Don Greive, PE
Additional contributions by Matt Postel and James R. Baty II, FACI, FTCA

The demand for office/warehouse and distribution facilities is as high as it has ever been. These structures vary in size from under 50,000 square feet to over a million square feet, and include single buildings and developments with multiple buildings. While some of these structures may be pre-engineered metal buildings with either metal-wall panels or tilt-wall panels, the preferred construction type utilizes load-bearing tilt-wall panels at the exterior with conventional steel framing at the interior. Usually, the steel construction makes use of tube columns with joists and joist girders at the roof. Unfortunately, a supply and demand imbalance is causing problems with acquisition of these components.

CURRENT SITUATION

In the current environment, these projects are facing multiple challenges regarding cost and schedule.  The primary source of these issues is related to the steel joists and joist girders. Prices have more than tripled in the past year, and lead times have also been extended. Current delivery estimates are seven to eight months from contracting. As a result, developers must spend more money and take more time, compared to a year ago, to deliver the same building. The impact on construction time can be close to three months depending on the project size.

The TCA has been pursuing the facts related to the severe challenges in the steel market since the beginning of this year. A thorough understanding of the causes as well as the potential term of impact has been developed over multiple conversations with major steel producers including Nucor, Worthington Steel, and Steel Dynamics. 

Initially, the first wave of the pandemic that resulted in a shut down across all markets had one of the largest impacts on manufacturing. As the foundries were forced to send the workforce home, the mills themselves went dormant or slowed to a creep. Although the dormancy was limited to a couple of months for most, the return to production required a graduated schedule. During this time, construction did not shut down for most markets and, in fact, barely slowed at all. Inventories were consumed and, by the time the mills were running at normal capacity, the damage was done. Multiple industries—including automotive, appliances, metal accessories, rolled stock, and nearly every secondary market for steel—could not order and receive enough steel to quench the demand. This has been further handcuffed by a global shortage of both iron ore and recycled steel, leaving steel mills with allocation percentages that are far less than their demand. The trickling down of an allocation reality impacts every manufacturing layer and distribution layer. There is far more demand than capacity for supply, and steel mills are focused on fulfillment of their contracts with little to no room for increased buys or what much of the construction industry uses: spot buys. This has resulted in frustration, hoarding, and lengthened delivery schedules.

With joist suppliers working multiple shifts on lines, it does not appear that delivery schedules or costs will improve in the near future. At current projections, the steel industry believes this challenge will be faced throughout 2021 and continue into as late as the second quarter of 2022. Therefore, it is time to consider some other options to steel joists and joist girders.

OPTIONS

There are several options, including alternatives to steel joists, that are available. The obvious path of least resistance would be to accept the cost increases and make schedule adjustments. That would likely require starting construction later to avoid the gap in the critical path when there would not be much activity while awaiting delivery of the joists/joist girders.

Another option would be to issue steel packages ahead of construction documents in order to lock in price and delivery earlier in the project’s schedule. This would only address a portion of the delivery delay and likely wouldn’t affect the higher cost. Also, this would frequently require a general contractor (GC) to be on board early in the project, which is not a model that all developers follow.

Of course, pre-engineered metal buildings (PEMBs) or the utilization of PEMB structural elements is another possibility. PEMBs would result in columns being installed around the perimeter of the building, which would encroach upon usable building space. Also, it is unclear if the market is willing to accept PEMBs as equivalent to a conventional steel building.

Another consideration could be to replace the joist girders with wide-flange beams. Beams are typically used in this way on projects without large bays. This may save some time on the schedule because deep joist girders have a larger impact on the schedule than typical joists, but joists will still have a long lead time.

There is another option available: the utilization of wide-flange sections in place of joists and joist girders. This option could return these projects back to the construction schedules of a year ago, possibly with a net cost savings over current prices.

STEEL BEAM OPTION

The use of steel wide-flange beams for roof structures has become attractive in today’s market.  Wide-flange shapes can be ordered to length from the mill and generally there are no complexities in the fabrication of these beams. However, there is more to do than simply picking a steel beam instead of a joist. Consideration must be given to the entire project, with an emphasis on the optimization of the design while considering several elements.

The first adjustment that is necessary when using steel beams is to change the deck. 3N deck should be utilized instead of the 1.5B. This allows the beams to be spaced apart significantly further than bar joists allow. With typical bays being 52’, 54’, or 56’, the ideal place to start on beam spacing is four spaces per bay. This results in a spacing between 13’ and 14’, which equates to beams being located at each tilt-wall panel joint, with one beam in between for most projects. Wind uplift pressures should be reviewed and checked with span tables. Also, FM Global requirements may affect the deck spans when conformance is required. Finally, we suggest consulting with deck vendors to confirm that deck lengths are available for a three-span condition. With the initial beam spacing determined, preliminary beam sizes can then be selected for the purlins and girders. We recommend considering using camber for these beams to help reduce the sizes.

Once the initial layout is determined, the diaphragm can be designed. Both the stiffness of the deck and the attachments should be evaluated. To optimize the budget, it is important to consider the cost of the deck, as well as the cost of the deck attachments including sidelap connectors. We have seen that 22-gage deck can be more cost effective than 20-gage deck—even with significantly more fasteners for attachment. Steel fabricators, erectors, and the deck suppliers are valuable resources in helping to optimize the deck design.

For the girders, it is possible to consider the use of cantilever/drop-in beams. Since the beams will be mill ordered, limitations on beam lengths do not need to be considered. If cantilever/drop-ins are being used, camber is not recommended. Also, bottom-flange braces would be required. If this system is utilized and results in the drop-in beams being shallower, we suggest reviewing that with the developers and brokers to make sure they do not see the change in depths as a deterrent to prospective tenants.

Partial Roof Plan with Cantilever/Drop-In Beams – Click to download PDF

With beams replacing bar joists, there would no longer be bridging at the roof. However, the beams need to be checked for uplift loads. In lieu of using angles with the increased spacing, smaller wide-flange beams can be utilized for bracing the bottom flanges of beams.

It is necessary to review the impact of beams on other trades involved in the project, especially regarding sprinkler requirements. The sprinkler contractor is the one whose work and cost is most affected by the change to beams. There are very specific requirements for sprinklers in these buildings, particularly regarding the distance of the heads from the bottom of the deck and the location of the heads. Sprinkler branch lines typically run through the joists near the deck. Therefore, there are two options with beams: One is to punch several holes in the webs of the beams to accommodate the sprinkler pipes at the same elevation that they would be at for joists. The other option is to run the pipes below the beams and use a vertical pipe to situate the heads at the proper elevations.

If the decision is made to punch holes in the beam webs, the fabricator’s equipment should be considered. Depending on the equipment, the holes could have minimal impact on a fabricator, or they could require significant time and expense. Also, the preferred pipe length for sprinkler branch lines is 21’. If the beam spacing is too close, that length of pipe cannot be installed and there will be increased costs due to the use of shorter pipes.

Another benefit of using beams is the potential adjustment in the top of steel elevations at the roof. The beam option will typically be shallower than the joist/joist-girder system. Therefore, there is the potential to lower the roof elevation while maintaining the same clear height requirements. The amount will vary with the geometry of the building, but could be in the range of approximately one foot. This could save one foot of panel height around the building, plus about 2%–3% on caulking expenses and costs involved with painting panels.

Regarding steel erection, there are significantly fewer members to install. Some erectors have successfully panelized sections of the roof on the ground to lift into place together. Potentially, a similar idea can be utilized with beams. We suspect that as the beam system is utilized on more projects, potential savings in erection costs may become available. When considering the cantilever/drop-in girder option, the erector should be consulted on the impact of panelizing, if that method is planned.

OTHER COST-SAVING IDEAS

There are some other ideas to consider that may reduce steel costs. However, one should note that some developers and brokers may not approve of these suggestions due to differing opinions on whether they would affect the marketability of the facility.

The first option is one that we have been suggesting for consideration for years. This would be to use a ½” per foot slope in the speed bays. Since required clear heights typically do not start until 6” past the first interior column line, joist and joist-girder sizes are not affected by this change. Instead, for a typical 60’ wide speed bay, there is a decrease in panel heights at the docks by 15”, resulting in cost savings at those panels.

The second option is to consider using wide-flange column sections instead of HSS/tubes. Currently, the price of tubes is more volatile than wide-flanges and it is higher per pound. Depending on available pricing and the particulars of the building, heavier wide-flanges may be available that would still be less expensive than tubes. For those requiring closed-in sections at columns, one consideration would be to add plates across the flanges in the lower sections of the wide-flange columns. Of course, this comes with a price and may make tubes a better option.

SUMMARY

The substitution of wide-flange beams for joists and joist girders is a good option in the current environment. How long this remains an option is dependent on the costs and lead times of joists and joist girders. It is important to consider fabrication and erection costs, as well as the impact on other trades, and to utilize this information in the optimization of the design. We recommend that you use the resources available to you (including your GC and relevant subcontractors) to aid in the design.

Unfortunately, there are not many projects available to use in a case study. In a few projects with the beam option rather than the joist option, we’ve found that steel costs for the shell building have experienced savings up to 14% and that the construction schedule saved significant time. Of course, the numbers can change quickly as joist costs continue to fluctuate. More information will be coming soon as the beam option is considered on more projects.

About the Authors

Don Greive, PE, is CEO of Pinnacle Structural Engineers, which is headquartered in Houston, Texas. Greive is a Top 50 Tilt-Up Industry Influencer and currently serves on the Tilt-Up Concrete Association’s board of directors.

Matt Postel is president at Postel Companies, which specializes in steel fabrication and erection in Texas.

James R. Baty II, FACI, FTCA, is the manager for regulatory and technical affairs for the Tilt-Up Concrete Association.

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