Ojai Municipal Code Art. 6 Analysis and Design

Except as modified herein, the analysis and design relating to the structural alteration of existing buildings shall be in accordance with the Uniform Building Code.

(§ 1, Ord. 678, eff. July 12, 1991)

(a) Buildings shall be analyzed by the general procedure of Section 9-12.603 of this chapter which is based on Chapter 23 of the Uniform Building Code or, when applicable, buildings may be analyzed by the special procedure of Section 9-12.604 of this chapter.

(b) URM buildings constructed of hollow concrete or clay tile shall be analyzed by the general procedure of Section 9-12.603 of this chapter unless it can be shown by testing that all masonry units were manufactured in compliance with Uniform Building Code Standard 24-4 or 24-8, as applicable, for bearing type units and that the capacity of the wall in bearing and shear, based on net area in contact through the bed joints, is not less than that allowed for solid bricks, in which case the special procedure of Section 9-12.604 of this chapter may be used.

(c) Buildings with a substantially completed concrete frame capable of supporting gravity dead and live loads and that utilize URM walls as non-bearing infill between frame members shall be analyzed by a procedure approved by the Building Official.

(d) Qualified URM historical buildings may be analyzed by either the general or special procedure of this chapter except that, as a means to preserve original architectural elements and facilitate restoration, an historical building may be analyzed in compliance with the State Historical Building Code.

(§ 1, Ord. 678, eff. July 12, 1991)

(a) Minimum design lateral forces. Buildings shall be analyzed to resist minimum lateral forces assumed to act non-currently in the direction of each of the main axes of the structure in accordance with the following:

(b) Lateral forces on elements of structures. Parts or portions of structures shall be analyzed and designed for lateral loads in accordance with Section 2312(g)2 of the Uniform Building Code. Exceptions:

(1) URM walls for which height to thickness ratios do not exceed ratios set forth in Table 12-B of this chapter need not be analyzed for out-of-plane loading. URM walls which exceed the allowable h/t ratios of Table 12-B of this chapter shall be braced according to Section 9-12.704 of this chapter.

(2) Parapets complying with Section 9-12.705 of this chapter need not be analyzed for out-of-plane loading.

(c) Shear walls (in-plane loading). Shear walls shall comply with Section 9-12.605

(§ 1, Ord. 678, eff. July 12, 1991)

(a) Limits for the application of this section. The special procedure of this section may be applied to buildings with the following characteristics:

(1) Flexible diaphragms at all levels above the base of structure;

(2) The vertical elements of the lateral force resisting system shall consist predominantly of masonry or concrete shear walls or steel braced frames or special moment resisting frames (See Section 2312 of the Uniform Building Code) each with a maximum overall height-to-length ratio of 1 ½ to 1;

(3) The lateral forces resisting systems shall be regular as defined in the Uniform Building Code. Except for a single-story building with an open front, a minimum of two lines of vertical lateral force-resisting elements shall be parallel to each axis of the building.

(b) Lateral forces on elements of structures. With the exception of the diaphragm provisions in this section, elements of structures shall comply with Section 9-12.603(b) of this chapter.

(c) Cross walls. Cross walls shall meet the requirements of this subsection:

(1) Cross wall definition. A cross wall shall mean a wood-framed wall sheathed with any of the materials described in Tables 12-C or 12-D of this chapter. Spacing of cross walls shall not exceed 40 feet on center measured perpendicular to the direction of consideration and shall be placed in each story of the building. Cross walls shall extend the full story height between diaphragms.

(2) Cross wall shear capacity. Within any 40 feet measured along the span of the diaphragm, the sum of the cross wall shear capacities shall be at least 30% of the diaphragm shear capacity of the strongest diaphragm at or above the level under consideration.

(3) Existing cross walls. Existing cross walls shall have a length to height ratio between openings of not less than 1:5. Existing cross wall connections to diaphragms need not be investigated as long as the cross wall extends to the framing of the diaphragm above and below.

(4) New cross walls. New cross wall connections to the diaphragm shall develop the cross wall shear capacity. New cross walls shall have the capacity to resist an overturning moment equal to the cross wall shear capacity times the story height. Cross wall overturning moments need not be cumulative over more than two stories.

(5) Other cross wall systems. Other systems such as special moment resisting frames may be used as cross walls provided that the yield story drift does not exceed one inch in any story.

(d) Wood diaphragms.

(1) Required analysis. An analysis of the diaphragm's capacity to control relative displacements between the shear walls need not be considered. Buildings that have an open front shall be analyzed for the relative displacement of the structure above the open front. The relative displacement may be considered to be adequately reduced by the installation of a shear wall at or closely adjacent to the open front in the level of the open front.

(2) Demand/capacity ratios. A building with an open front on one side may have cross walls parallel to the open front and shall be designed by the following procedure:

(i) Effective diaphragm span, Li, for use in Figure No. 12-1 shall be determined in accordance with the following formula:

(ii) Diaphragm demand/capacity ratio shall be calculated as:

(iii) If cross walls are used, the demand/capacity ratio shall be calculated as:

(3) Chords. An analysis for diaphragm flexure need not be made and chords need not be provided.

(4) Collectors. An analysis of diaphragm collector forces shall be made for the transfer of diaphragm edge shears into vertical elements of the lateral force resisting system. Collector forces may be resisted by new or existing elements.

(5) Diaphragm openings.

(i) Diaphragm forces at corners of openings shall be investigated and shall be developed into the diaphragm by new or existing materials.

(ii) Openings in the diaphragm of a maximum of one-half of the diaphragm span in the middle half of the diaphragm span or one-quarter (¼) of the diaphragm depth in the end one-quarter of the diaphragm span need not be considered a discontinuity.

(iii) Roof or floor diaphragms that are discontinuous shall be modified to provide a continuous load path from every part or portion of the building to the ground. A continuous load path for a discontinuous diaphragm may be provided by infilling the openings with any new materials that are equal to the existing diaphragm materials.

(iv) Shear walls or cross walls may be provided at the discontinuous edge or the diaphragm. If cross walls are provided, the analysis procedures for open front buildings shall be used.

(6) Diaphragm shear transfer. Diaphragms shall be connected to shear walls with connections capable of developing a minimum force calculated by the lesser of the following formulae:

(i) V =.5Z Cp Wd using Cp values of Table 12-A; or

(ii) V = v4D

(e) In-plane loading—URM walls.

(1) Wall story force. For buildings without cross walls, the wall story force distributed to a shear wall at a diaphragm level shall be the lesser value calculated as:

but need not exceed

(2) Wall story shear. The wall story shear shall be the sum of the wall story forces at and above the level of consideration.

(3) Shear wall analysis. Shear walls shall comply with Section 9-12.605 of this chapter.

(4) Moment frames. Moment frames used in place of shear walls shall be designed as required in Chapter 23 of the Uniform Building Code except that the forces shall be as specified in subsection (e)(1) of this section and the interstory drift ratio shall be limited to 0.005.

(f) Out-of-plane loading—URM walls.

(1) Allowable URM wall height-to-thickness ratios. The allowable h/t ratios given in Table 12-B of this chapter shall be used. URM walls which exceed the allowable h/t ratios of Table 12-B of this chapter shall be braced according to Section 9-12.704 of this chapter.

(2) Parapets. Parapets complying with Section 9-12.705 of this chapter need not be analyzed for out-of-plane loading.

(§ 1, Ord. 678, eff. July 12, 1991)

The following shall be applicable to both general procedure and special procedure buildings:

(a) Required analysis. Buildings that have an open front shall be analyzed for the in-plane shear strength of the URM shear wall(s) parallel to the open front.

(b) Existing URM walls.

(1) Flexural rigidity. Flexural rigidity may be neglected in determining the rigidity of a URM wall.

(2) Shear walls with openings. For any pier, wall piers shall be analyzed according to the following procedure:

(i) The pier shear capacity shall be calculated as:

(ii) The pier rocking shear capacity shall be calculated as:

(iii) The wall piers at any level are acceptable if they comply with one of the following modes of behavior:

i. Rocking mode. Where all piers at a level have shear capacities capable of sustaining rocking, i.e., the pier shear capacity is greater than or equal to the pier rocking shear capacity for each pier, forces in the wall at that level, Vwx, shall be distributed to each pier, Vp, in proportion to PDD/H.

For each pier at that level:

and for the wall at that level:

ii. Non-rocking mode. Where at least one pier at a level is incapable of sustaining a rocking mode, i.e., the pier shear capacity is less than the pier rocking shear capacity, forces in the wall at that level, Vwx, shall be distributed to each pier, Vp, in proportion to D/H, such that Vwx = ΣVp.

For at least one pier at that level:

For each pier at that level:

If Vp > Vr in one or more piers, omit such piers from the analysis and repeat the procedure for the remaining piers or strengthen and re-analyze the wall.

iii. Masonry pier tension stress. URM wall piers need not be analyzed for tension stress.

(3) Shear walls without openings. Shear walls without openings shall be analyzed as for walls with openings except that Vr shall be calculated as follows:

(c) Plywood sheathed shear walls. Plywood sheathed shear walls may be used to resist lateral loads for buildings with flexible diaphragms analyzed according to provisions of Section 9-12.603 of this chapter. Plywood sheathed shear walls may not be used to share lateral loads with other materials along the same line of resistance.

(d) Combinations of vertical elements.

(1) Lateral force distribution. Lateral forces shall be distributed among the vertical resisting elements in proportion to their relative rigidities except that moment frames shall comply with subsection (d)(2) of this section.

(2) Moment resisting frames. A moment resisting frame shall not be used with a URM wall in a single line of resistance unless the wall(s) have piers that are capable of sustaining rocking in accordance with subsection (b) of this section and the frames are designed to carry 100 percent of the lateral forces.

(§ 1, Ord. 678, eff. July 12, 1991)