Understanding Live Loads in Parking Garages: What About Electrical Car

Introduction

When designing parking garages, accounting for live loads is essential. The required live load values differ greatly depending on whether the structure serves passenger vehicles or heavier vehicles, such as trucks and buses. In this article, we will explore how design live loads are calculated and touch on the potential influence of electric vehicles on parking garage design considerations.

Live Loads for Passenger Vehicle Garages

For parking garages designed for passenger vehicles—including cars, SUVs, and pickup trucks with a gross vehicle weight rating up to 44.5 kN—the 2024 International Building Code (IBC) specifies a minimum uniformly distributed live load of 1.9 kN/m² (Table 1607.1). This load generally cannot be reduced under the code’s live load reduction provisions, except for vertical members supporting two or more floors, where a reduction of up to 20% is allowed. The same minimum live load is also specified in ASCE 7-22 (Table 4.3-1). Historically, prior to ASCE 7-02, passenger vehicle garages required a uniformly distributed live load of 2.4 kN/m², subject to reduction. In ASCE 7-02, this was reduced to 1.9 kN/m² non-reducible, based on a 2001 study by Y. K. Wen at the University of Illinois at Urbana-Champaign.

ASCE 7-02 Commentary Section C4.8.3 explained that:

“…Compared with the design live load of 2.4 kN/m2 given in previous editions of ASCE 7, a 1.9 kN/m2 live load represents a 20% reduction but is still 33% higher than the 1.4 kN/m2 one would obtain were an area-based reduction to be applied to the 2.4 kN/m2 value for large bays.”

Both the 2024 IBC and ASCE 7-22 account for concentrated loads in addition to uniform loads. While these concentrated loads usually don’t control the design, engineers should always check whether they could be critical in specific situations.

For garages designed for passenger vehicles carrying up to nine passengers, a single concentrated load of 13.3 kN acting on an area of 112.5 mm × 112.5 mm must be considered. This load simulates the force applied by a jack when changing a tire on a single vehicle. The load should be positioned to produce the maximum effect on the structural member under consideration. In some cases, this concentrated load may govern the punching shear design of garage slabs or the flexural design of double-T sections, particularly when applied near the end of the flange.

For mechanical parking structures without slabs or decks, designed to store passenger vehicles only, a concentrated load of 10 kN per wheel must be applied.

Designing Parking Garages for Heavy Vehicles: Live Load Requirements

For garages accommodating heavy vehicles—those with a gross vehicle weight rating over 44.5 kN, including trucks, buses, fire trucks, emergency vehicles, forklifts, and other movable equipment—live load requirements are provided in Section 1607.8 of the 2024 IBC.

Structural elements or areas where heavy vehicles may be driven must be designed using vehicular live loads in accordance with locally adopted codes for roadway and bridge design, such as the AASHTO LRFD Bridge Design Specifications. Section 1607.8.1 of the 2024 IBC also requires consideration of impact and fatigue effects in these cases.

However, for structures intended solely for parking heavy vehicles, such as dedicated heavy vehicle garages, impact and fatigue design is not required (Section 1607.8.3). Additional guidance is provided in ASCE 7-22 Commentary Section C4.10.2.

…For heavier trucks and buses, the vehicular live loads in the AASHTO LRFD Bridge Design Specifications (AASHTO) are to be applied. The AASHTO provisions for fatigue and dynamic load allowance are not required to be applied as the vehicle speeds in garages and vehicle storage areas are much lower than typical highway speeds.

Electric Vehicles and Parking Garage Design: How Live Loads Are Affected

The rise of electric vehicles (EVs), which made up over 10% of U.S. passenger vehicle sales in 2024, has raised questions about whether current parking garage live load standards are sufficient. While EVs are still under 2% of vehicles on the road, their heavier weight—similar to the trend toward SUVs and pickups—could affect load assumptions. Ongoing research, including a new study funded by the Charles Pankow Foundation, is examining how increasing EV adoption may influence parking garage design.

A major concern regarding electric vehicles (EVs) is the risk of fire caused by battery thermal runaway. Thermal runaway is an uncontrolled, self-heating process in which a battery’s temperature rises rapidly, potentially resulting in fire or explosion. Fires involving EVs have proven to be more difficult to extinguish than those in traditional internal combustion engine vehicles. Research by the Fire Protection Research Foundation indicates that while EV fires may develop more slowly and do not reach the same peak intensity, they tend to burn for much longer durations. It may take several years before any recommendations arising from ongoing structural and fire safety research are adopted as mandatory building code requirements.

Reference:

(https://www.structuremag.org/article/electrical-vehicles-and-parking-structures/)