Designing Steel Towers for Saudi Arabia: SBC and IBC Together

The SBC–IBC Relationship

The Saudi Building Code (SBC) adopts much of IBC's structural framework as its technical backbone but overlays kingdom-specific provisions for seismic hazard, wind, and materials. The key document for structural steel is SBC 306 (Structural Steel Design), which directly references AISC 360 with modifications. Load provisions come from SBC 301, which is calibrated to IBC's ASCE 7 methodology but uses Saudi-specific hazard maps.

For steel tower projects — entertainment structures, observation decks, amusement ride supports — engineers must satisfy both bodies simultaneously. Wherever SBC is silent, IBC governs. Wherever SBC is explicit, SBC overrides.

Seismic Zones in Saudi Arabia

Saudi Arabia spans three seismic regions under SBC 301:

• Western Region (Hejaz/Asir): Moderate seismicity — Ss up to 1.0 g, S1 up to 0.4 g near the Red Sea escarpment. Aqaba fault zone elevates risk for some Tabuk and Haql sites.
• Central/Eastern Region (Riyadh, Dammam, Jubail): Low seismicity. Ss typically 0.1–0.3 g, S1 below 0.1 g. Seismic Design Category A or B for most structures.
• Farasan Archipelago and Gulf shores: Negligible seismicity for standard structures.

The Dammam entertainment tower we designed (Eastern Province) fell into SDC B — seismic loads were secondary to wind. The governing lateral load was wind at 45 m/s basic wind speed per SBC 301 wind map.

Wind Design Under SBC 301

SBC 301 uses a 50-year mean recurrence interval wind map for the Arabian Peninsula, derived from regional meteorological records. Basic wind speeds range from 34 m/s in sheltered inland regions to 50+ m/s along exposed coastal and highland sites. The conversion to ASCE 7's 3-second gust speed format is already embedded in SBC tables — no conversion required.

Exposure categories follow the same Exposure A/B/C/D classification as ASCE 7, but Exposure D (flat unobstructed terrain near large water bodies) applies much more frequently in KSA given the Arabian Gulf and Red Sea coastlines. Most tower projects near Dammam or Jeddah default to Exposure D without exception.

For towers, the velocity pressure equation remains:

q_z = 0.613 × K_z × K_zt × K_e × V²  (N/m², V in m/s)

The topographic factor K_zt is often the source of disagreement between designers and review authorities. Escarpment sites in Asir require careful topographic surveys; flat Riyadh and Dammam sites default to K_zt = 1.0.

Load Combinations: SBC 301 vs IBC LRFD

SBC 301 uses LRFD combinations directly from ASCE 7-16, with one key addition: a sand/dust accumulation load of 0.5 kN/m² on horizontal surfaces in designated sandstorm zones (primarily central and northwestern Arabia). This load is added as a live-load component (denoted S_d in SBC notation) and appears in combinations as:

1.2D + 1.6S_d + 1.0L + 0.5(L_r or S or R)
1.2D + 1.0W + 1.0L + 0.5S_d

For amusement and entertainment structures, occupancy category III is standard (large public assembly, >300 persons), elevating the importance factor I_e to 1.25 for seismic and I_w to 1.15 for wind.

Steel Material Specifications

SBC 306 permits ASTM A36, A572 Gr.50, A992, and equivalent SASO-certified steels. In practice, most Saudi fabricators stock European S275/S355 sections (EN 10025) because of procurement chains through Europe and Asia. SBC 306 explicitly allows EN material grades with an equivalence demonstration:

• S275 ≈ A36 (F_y = 250–275 MPa)
• S355 ≈ A572 Gr.50 (F_y = 345–355 MPa)

Design calculations in AISC 360 notation (kips, inches) must be converted when using EN-sourced steel and metric sections. We maintain a single unit system throughout — SI metric when working with Saudi/European suppliers, converting only for AISC equation check values. This prevents the unit-mixing errors that cause the most calculation mistakes in cross-code practice.

Welding and Connection Standards

Connection design for KSA projects follows AISC 360 Chapter J, with weld procedures qualified per AWS D1.1. Saudi Aramco projects add their own SAES-S-series supplemental requirements; non-Aramco projects use the SBC 306 baseline. Bolted connections in high-wind zones require slip-critical design (Class A faying surface, fully tensioned ASTM A325 or equivalent ISO 8.8 bolts). Saudi fabricators are fully capable of meeting this specification — the issue is ensuring the inspection regime (bolting torque records, VT/UT reports) is contractually required and actually enforced on site.

The Dammam Entertainment Tower: Compliance Path

For the Dammam entertainment tower, our compliance path was:

1. Establish site seismic hazard: SDC B (confirmed from SBC 301 maps, Ss = 0.25 g)
2. Obtain municipality wind speed letter: 45 m/s, Exposure D
3. Confirm dust accumulation applies: 0.5 kN/m² on horizontal observation platforms
4. Select S355 plate and S275 wide-flange sections from local supplier
5. Perform AISC 360 member design with converted metric inputs
6. Design slip-critical connections per AISC 360 J3, AWS D1.1 weld procedures
7. Issue bilingual design report (English + Arabic) with SBC 2018 stamp reference

The bilingual report requirement is informal but practically mandatory — the municipality review team reads Arabic and the client's international EPC contractor reads English. Providing both eliminates back-and-forth translation delays.

Common Mistakes in KSA Steel Tower Design

After multiple KSA projects, the same errors recur:

• Using ASCE 7 wind maps instead of SBC 301: ASCE 7-22 maps are calibrated to US climatology. Use SBC 301 wind maps only.
• Omitting dust load: 0.5 kN/m² is small but consistent municipality rejection item when missing.
• Ignoring the SBC edition: SBC 2007 and SBC 2018 differ in seismic provisions. Specify the edition explicitly.
• Mixing ASTM and EN material in same connection: ASTM A490 bolts with EN plate — the surface hardness interaction must be checked per AWS D1.1 notes.
• SDC A treatment for all Eastern Province: Most of EP is SDC A, but Gulf-facing coastal strips occasionally reach SDC B. Always compute from site coordinates, never from regional assumption.

Frequently Asked Questions