Structural Design Frequently Asked Questions

2016 California Building Code (CBC)

1. All SMRF moment connection pre-qualifications are for beam orthogonal to column. Does OSHPD permit a beam to be at an angle to column?

No. However, for a deep beam with heavy W14 column, OSHPD may permit a beam to have very slight angle to column not to exceed 5 degrees. It is preferred that the skew angle be accommodated at the first lateral brace point required for the beam bottom flange where the out-of-plane force due to the concentrated skew angle is resisted by a perpendicular brace beam into the diaphragm.

2013 California Building Code (CBC)

1. Can OSHPD Preapproval of Anchorage (OPA) based on the 2001, 2007, or 2010 CBC be used on projects governed by the 2013 CBC?

No.

2. Can OSHPD Preapproval of Manufacturer′s Certification (OPM) based on the 2013 CBC be used on projects governed by the 2001, 2007, or 2010 CBC?

Yes.

3. Section 1616A.1.13 requires scaling of modal base shear (base shear calculated by the response spectra method) upward to the equivalent static base shear. Can the modal base shear be scaled down?

No. If the calculated modal base shear is higher than the equivalent static base shear it cannot be reduced.

ASCE 7-10, Section 12.9.2 permits modal base shear to be calculated by using response spectra defined in either Section 11.4.5 or 21.2 in ASCE 7-10 divided by the quantity R/Ie.

4. Section 11.2 of ASCE 7-10 defines a bearing wall as any metal or wood wall that supports more than 100 lb./linear ft. of vertical load in addition to its own weight and any concrete or masonry wall that supports more than 200 lb./linear ft. of vertical load in addition to its own weight. Does this definition apply to Table 12.2-1, Design Coefficients and Factors for Seismic Force-Resisting Systems in ASCE 7-10?

Yes. Definitions in Section 11.2 of ASCE 7-10 apply to all seismic requirements in the 2013 CBC and ASCE 7-10, unless modified in the 2013 CBC.

5. Section 12.8.7 of ASCE 7-10 permits β (the ratio of shear demand to shear capacity for the story) to be conservatively taken as 1.0. For steel special moment resisting frams (SMRF), with Cd = 5.5 and β = 1, θmax = 0.09, which is less than 0.10. Does this mean that P-Δ effects need not to be considered for steel SMRF design?

No. P-Δ effects shall be considered for all steel frame design as required by Section C1 of AISC 360-10 and for all concrete frame design as required by Sections 10.10 through 10.13 of ACI 318-11. See Section 1.1.7 of the 2013 CBC.

6. Are the site-specific spectra required for all modal response spectrum analysis under the 2013 CBC?

No. Site-specific spectra are only required when specified in CBC Section 1616A.1.3. However, site-specific spectra may be used for any structure.

7. Does OSHPD permit an increase in drift limit to 125% of the drift limit specified in Section 12.12.1 of ASCE 7-10, as allowed in Section 16.2.4.3 of ASCE 7-10?

Yes.

8. Does seismic bracing (supports and attachments) of distribution system require a deferred submittal or will these submittals be consistently triaged and field approved by the Office?

An item is never required to be submitted as deferred submittal. However, for systems that are often designed by the vendors or specialty contractors, such as distribution system seismic bracing (supports and attachments), deferred submittals are common. OSHPD Preapproval of Manufacturer′s Certification (OPM) may be used for the supports and attachments of pipes, conduits and ducts. A Registered Design Professional (RDP) has designed the OPM and OSHPD has reviewed the supporting documents for code compliance. Therefore, the OPM and supporting documents are not to be re-reviewed by OSHPD regional staff. However, each distribution system OPM requires submittals that shall be reviewed and approved by OSHPD on project specific basis to ensure that: 

Structure Supporting the distribution system has adequate capacity;
Seismic design forces (Fp) are in accordance with the CBC 2013; and
Submittal is within the scope of OPM for:
Size of distribution system components,
Spacing of bracing and flex joints, and
Substrate for attachments.
As with all OPMs, construction documents are still required showing how and where the OPM will be applied to each applicable system on a project specific basis.

The distribution system OPM typically relies on a prescriptive approach. The OPMs have tables and charts associated with them that shall be used to select the appropriate detail for each location that a support/attachment is to be installed. The application of these criteria should never become the responsibility of the IOR, whose responsibility is to inspect only, not design.
The structural engineer of record is required to review and forward the supports and attachments construction documents for OSHPD review …with a notation indicating that the construction documents have been reviewed and they have been found to be in general conformance with the project requirements; see CAC Section 7-153. A “shop drawing stamp” is usually acceptable for compliance with this requirement.
The OSHPD regional staff, on a project specific basis, will review supports and attachments detail and supporting documents that are not part of an OPM. Review of supports and attachments of this nature do not constitute a pre-approval that may be used on other projects without the benefit of OSHPD construction documents review.

2007 California Building Code (CBC)

1. Can OSHPD Preapprovals (OPA) based on the 2001 CBC be used on projects governed by the 2007 CBC?

Yes. Existing OSHPD Preapprovals (OPA) based on the 2001 CBC may be used without modification on projects subject to the 2007 CBC. All aspects of the design and installation of the preapproval component or system, including computation of the lateral forces, shall be in accordance with the approved OPA.

2. Section 1614A.1.9 requires scaling of modal base shear (base shear calculated by the response spectra method) upward to the equivalent static base shear. Can the modal base shear be scaled down?

No. If the calculated modal base shear is higher than the equivalent static base shear, the design must be based on the modal base shear without reduction.

ASCE 7-05, Section 12.9.2 permits modal base shear to be calculated by using response spectra defined in either Section 11.4.5 or 21.2 in ASCE 7-05 divided by the quantity R/I.

3. Section 11.2 of ASCE 7-05 defines a bearing wall as any metal or wood wall that supports more than 100 pound/linear foot of vertical load in addition to its own weight and any concrete or masonry wall that supports more than 200 pound/linear foot of vertical load in addition to its own weight. Does this definition apply to Table 12.2-1, Design Coefficients and Factors for Seismic Force-Resisting Systems in ASCE 7-05?

Yes. Definitions in Section 11.2 of ASCE 7-05 apply to all seismic requirements in the 2007 CBC and ASCE 7-05, unless modified in the 2007 CBC.

4. Section 12.8.7 of ASCE 7-05 permits β (the ratio of shear demand to shear capacity for the story) to be conservatively taken as 1.0. For steel special moment resisting frames (SMRF), with Cd = 5.5 and β = 1, θmax = 0.09, which is less than 0.10. Does that mean that no P-Δ effects need to be considered for steel SMRF design?

No. P-Δ effects shall be considered for all steel frame design as required by Section C1 of AISC 360-05 and for all concrete frame design as required by Sections 10.10 through 10.13 of ACI 318-05. See Section 101.7.2 of the 2007 CBC.

5. Are the site-specific spectra required for all modal response spectrum analysis under the 2001 CBC?

No. Site-specific spectra are only required when specified in CBC Section 1614A.1.2. However, site-specific spectra may be used for any structure.

6. Does OSHPD permit an increase in drift limit to 125% of the drift limit specified in Section 12.12.1 of ASCE 7-05, as allowed in Section 16.2.4.3 of ASCE 7-05?

Yes, provided an analysis is performed as required by ASCE 7-05, Chapter 16 and the 2007 CBC, Section 1614A.

7. How does one go about calculating the building separation in accordance with Section 12.12.3 of ASCE 7-05?

The building separation between two buildings may be calculated as the algebraic sum of the total deflection (δx) of the two buildings as determined in Section 12.8.6 (Equation 12.8-15) of ASCE 7-05.

8. Can the strength reduction factor of resistence factor, φ, be taken as 1.0 when using load combinations with overstrength factor or when seismic forces are amplified by the system overstrength factor, Ω0?

No. However, for Allowable Stress Design (ASD) load combinations with the overstrength factor, an increase in allowable stress is permitted by Section 12.4.3.3 of ASCE 7-05.

9. Does OSHPD permit wind load calculations based on the Division of the State Architect (DSA), Interpretation of Regulations (IR) #16-7, Wind Load Determination – Alternate Method?

No. However, OSHPD has amended the 2007 CBC to adopt simplified wind load provisions. See 2007 CBC, Sections 1609.1.1 and 1609A.1.1.

10. Can we use the Seismic Load Effect including Overstrength Factors as shown in Section 12.4.3 of ASCE 7-05 instead of the Special Seismic Load Combinations shown in Section 16505A.4 of the 2007 CBC?

Yes. Special Seismic Load Combinations in Section 1605A.4 of the 2007 CBC were revised in the 2007 Supplements to the 2006 International Building Code (IBC) for consistency with ASCE 7-05. There are additional proposals to further modify the IBC prior to publication of the 2009 edition.

11. Does seismic bracing of overhead utilities require a deferred submittal or will these submittals consistently be triaged and field approved by the Office?

An item is never required to be submitted as a deffered submittal; however, for systems that are often designed by the vendors or specialty contractors, such as seismic bracing, dererred submittals are common. Pre-approved systems may be used for the anchorage and bracing of pipes, conduits and ducts. A California Licensed Structural Engineer has designed the pre-approved systems, along with supporting calculations. Therefore, the pre-approved details and calculations are not to be re-reviewed by regional staff. However, each pre-approved system requires submittals that must be reviewed and approved by OSHPD.

As with all pre-approved details systems, etc., plans are still required showing how and where the pre-approved anchorage and bracing systems will be applied to each applicable system on a project specific basis. This process is needed to verify that the appropriate detail has been selected and applied for each condition and for the actual substrate that it will be connected/attached to. Depending on the system to be anchored and/or braced, these plans may be prepared by an architect or engineer. See California Administrative Code (CAC) Section 7-115.

The pre-approved systems typically rely on a prescriptive cookbook approach. The pre-approved details have tables and charts associated with them that must be used to select the appropriate detail for each location that an anchor or brace is to be installed. The application of these criteria should never become the responsibility of the Inspector of Record (IOR), whose responsibility is to inspect only, not design.

The structural engineer of record must review and forward the anchorage and bracing plans for plan check with a notation indicating that the plans have been reviewed and they have been found to be in general conformance with the design of the project; See CAC Section 7-153 (d). A “shop drawing stamp” is usually acceptable for compliance with this requirement.

The regional staf, on a project specific basis, must review anchorage and bracing details and supporting calculations that are not part of a pre-approved system. Review of anchorage and bracing details of this nature do not constitute a pre-approval that may be used on other projects without the benefit of plan review.