Background

Before 2007, structural engineers in Saudi Arabia primarily relied on British or American codes, depending on their educational background, as there was no unified national code for building design. Additionally, the Uniform Building Code (UBC) provided only limited seismic zone data for a few cities in Saudi Arabia.

With the publication of the Saudi Building Code (SBC) in 2007, a clear, standardized framework was established to meet local requirements. However, despite the availability of SBC, three common mistakes persist among structural engineers when applying the code.

1. Mixing Code Requirements

Many structural engineers in Saudi Arabia currently use IBC 2012 / ASCE 7-10 standards alongside the wind and seismic maps provided in the SBC. However, SBC is actually based on IBC 2003 / ASCE 7-02. This mismatch can lead to underestimating wind design loads, potentially resulting in structural failures.

Key Differences Between ASCE 7-02 and ASCE 7-10:

Wind Speed Representation:

ASCE 7-10 uses “ultimate” wind speeds for strength design.

SBC uses “service” wind speeds, which are lower.

Wind Load Factor:

ASCE 7-10 applies a load factor of 1.0 for wind.

SBC follows ASCE 7-02, which applies a load factor of 1.6.

This discrepancy means that using ASCE 7-10 values directly with SBC load combinations can lead to an unsafe design.

Load Combinations as per ASCE 7-10:

Text showing basic combinations for design strength with equations such as 1.4D, 1.2D + 1.6L + 0.5(Lr or S or R), 1.2D + 1.6(Lr or S or R) + (L or 0.5W), and 1.2D + 1.0W + L + 0.5(Lr or S or R).

Text from a structural engineering document featuring load combinations for design. Includes equations 2.3.2-1 to 2.3.2-7 with factors such as 1.4 (D + F), 1.2D, 1.6W, and others. Highlights include '1.6W' and '0.8 W'. The section outlines conditions for different load scenarios, with specific factors given for public assembly areas or parking garages.

Therefore, to correctly use ASCE 7-10, the wind speed must be adjusted accordingly.

Fortunately, ASCE 7-10 includes a table in the commentary to facilitate the transition, providing a conversion between strength-level wind speeds and service-level wind speeds from ASCE 7-05, as shown below:

Table displaying design wind speeds according to ASCE standards 7-05, 7-10, and 7-93, with respective speeds in mph.

2. Missing Load Combination

The Saudi Building Code (SBC) specifies load combinations in Section 2.3.2. However, an additional load requirement for designing concrete and masonry structures is stated in Exception Clause No. 2, which is often overlooked by engineers.

Text document outlining exceptions for load factors in concrete and masonry construction, featuring highlighted equations for load combinations.

3. Design Coefficients and Factors for Basic Seismic Force-Resisting Systems

The Saudi Building Code (SBC) uses lower values for the Response Modification Coefficient (R), Seismic Overstrength Factor (Ω), and Deflection Amplification Factor (Cd) compared to the International Building Code (IBC).

A new version of the SBC is currently under review and is expected to be released by the end of this year.

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