The coefficient R in computing for base shear in static force method represents the inherent over-strength and global ductility capacity of lateral-force-resisting systems.
There are 4 tables for this value (Table 208-11), categorized with the different materials used for the frames - for concrete, steel, masonry, and wood. Different tables contain the different seismic-force resisting system namely:
1. Bearing-wall systems. Structural systems where building loads (dead and live looads) are transferred to the ground through walls.
2. Building frame systems. Structural systems with complete space frames to support vertical loads.
Note: The value of R for building frame systems is greater than that assigned to bearing wall systems, thus the former is more desirable from a cost-efficient design perspective.
3. Moment-resisting frames. Rectilinear Structural assemblages of beams and columns with beams rigidly connected to the columns.
4. Dual systems. Structural systems where a complete frame provides support from gravity loads. Lateral loads support is provided by moment -resisting frame ad braced frames of shear walls.
5. Cantilevered column building frames. Seismic force-resisting systems whereby lateral loads are resisted by columns acting as vertical cantilevers.
6. Shear-wall frame interaction systems. Structural systems with combination of shear walls and frames to provide the required stiffness and strength in withstanding loads in high rise buildings.
NSCP uses moment-resisting frames, particularly special moment resisting frames. The other two kids of these kinds of frames are ordinary and intermediate.
- Ordinary moment resisting frames do not meet special detailing requirements for ductile behavior.
- Intermediate moment resisting frames are concrete or steel frames designed in accordance to section 8.3 in BNBC 93.
- Special moment resisting frame is specially detailed to provide ductile behavior complying with seismic requirements provided in BNBC 93.
NSCP specifies using Special moment resisting frames for analysis and study on lateral loads.
TABLE 208-11A Earthquake-force-resisting Structural Systems of Concrete
TABLE 208-11A Earthquake-force-resisting Structural Systems of Concrete
| BASIC SEISMIC-FORCE RESISTING SYSTEM | R |
|---|---|
| A. BEARING WALL SYSTEMS | |
| Special reinforced concrete shear walls | 4.5 |
| Ordinary reinforced concrete shear walls | 4.5 |
| B. BUILDING FRAME SYSTEMS | |
| Special reinforced concrete shear walls or braced frames (shear walls) | 5 |
| Ordinary reinforced concrete shear walls or braced frames | 5.6 |
| Intermediate precast shear walls or braced frames | 5 |
| C. MOMENT-RESISTING FRAME SYSTEMS | |
| Special reinforced concrete moment frames | 8.5 |
| Intermediate reinforced concrete moment frames | 5.5 |
| Ordinary reinforced concrete moment frames | 3.5 |
| D. DUAL SYSTEMS | |
| Special reinforced concrete shear walls | 8.5 |
| Ordinary reinforced concrete shear walls | 6.5 |
| E. DUAL SYSTEM WITH INTERMEDIATE MOMENT FRAMES | |
| Special reinforced concrete shear walls | 6.5 |
| Ordinary reinforced concrete shear walls | 5.5 |
| Shear wall frame interactive system with ordinary reinforced concrete | |
| moment frames and ordinary reinforced concrete shear walls" | 4.2 |
| F. CANTILEVERED COLUMN BUILDING SYSTEMS | |
| Cantilevered column elements | 2.2 |
| G. SHEAR WALL-FRAME INTERACTION SYSTEMS | 5.5 |
TABLE 208-11B Earthquake-force-resisting Structural Systems of Steel
| BASIC SEISMIC-FORCE RESISTING SYSTEM | R |
|---|---|
| A. BEARING WALL SYSTEMS | |
| Light steel-framed bearing walls with tension-only bracing | 2.8 |
| Braced frames where bracing carries gravity load | 4.4 |
| Light framed walls sheathed with steel sheets structural panels rated for | |
| shear resistance or steel sheets | 5.5 |
| Light-framed walls with shear panels of all other light materials | 4.5 |
| Light-framed wall systems using flat strap bracing | 2.8 |
| B. BUILDING FRAME SYSTEMS | |
| Steel eccentrically braced frames (EBF), moment resisting connections at | |
| at columns away from links | 8.0 |
| Steel eccentrically braced frames (EBF), non-moment-resisting connections | |
| away from links | 6.0 |
| Special concentrically braced frames (SCBF) | 6.0 |
| Ordinary concentrically braced frames (OCBF) | 3.2 |
| Light-framed walls sheathed with steel sheet structural panels/sheet steel | |
| panels | 6.5 |
| Light frame walls with shear panels of all other materials | 2.5 |
| Buckling-restrained braced frames (BRBF), non-moment-resisting | |
| beam-column connection" | 7.0 |
| Buckling-restrained braced frames, moment-resisting beam-column connections | 8.0 |
| Special steel plate shear walls (SPSW) | 7.0 |
| C. MOMENT-RESISTING FRAME SYSTEMS | |
| Special moment-resising frame (SMRF) | 8.0 |
| Intermediate steel moment frames (IMF) | 4.5 |
| Ordinary moment frames (OMF) | 3.5 |
| Special truss moment frames (STMF) | 6.5 |
| Special composite steel and concrete moment frames | 8.0 |
| Intermediate composite moment frames | 5.0 |
| Composite partially restrained moment frames | 6.0 |
| Ordinary composite moment frames | 3.0 |
| D. DUAL SYSTEMS WITH SPECIAL MOMENT FRAMES | |
| Steel eccentrically braced frames | 8.0 |
| Special steel concentrically braced frames | 7.0 |
| Composite steel and concrete eccentrically braced frame | 8.0 |
| Composite steel and concrete concentrically braced frame | 6.0 |
| Composite steel plate shear walls | 7.5 |
| Buckling-restrained braced frames (BRBF), non-moment-resisting | |
| beam-column connection" | 8.0 |
| Special steel plate shear walls | 8.0 |
| Masonry shear wall with steel OMRF | 4.2 |
| Steel EBF with steel SMRF | 8.5 |
| Steel EBF with steel OMRF | 4.2 |
| Special concentrically braced frames with steel SMRF | 7.5 |
| Special concentrically braced frames with steel OMRF | 4.2 |
| E. SUAL SYSTEM WITH INTERMEDIATE MOMENT FRAMES | |
| Special steel concentrically braced frame | 6.0 |
| Composite steel and concrete concentrically braced frame | 5.5 |
| Ordinary composite braced frame | 3.5 |
| Ordinary composite reinforced concrete shear walls with steel elements | 5.0 |
| F. CANTILEVERED COLUMN BUILDING SYSTEMS | |
| Special steel moment frames | 2.2 |
| Intermediate steel moment frames | 1.2 |
| Ordinary steel moment frames | 1.0 |
| Cantilevered column elements | 2.2 |
| G. STEEL SYSTEMS NOT SPECIFICALLY DETAILED FOR SEISMIC RESISTANCE, | |
| EXCLUDING CANTILEVER SYSTEMS | 3.0 |
TABLE 208-11C Earthquake-force-resisting Structural Systems of Masonry
| BASIC SEISMIC-FORCE RESISTING SYSTEM | R |
|---|---|
| A. BEARING WALL SYSTEMS | |
| Masonry shear walls | 4.5 |
| B. BUILDING FRAME SYSTEMS | |
| Masonry shear walls | 5.5 |
| C. MOMENT-RESISTING FRAME SYSTEMS | |
| Masonry moment-resisting wall frames (MMRWF) | 6.5 |
| D. DUAL SYSTEMS | |
| Masonry shear walls with SMRF | 5.5 |
| Masonry shear walls with OMRF | 4.2 |
| Masonry shear walls with concrete IMRF | 4.2 |
| Masonry shear walls with masonry MMRWF | 6.0 |
TABLE 208-11D Earthquake-force-resisting Structural Systems of Wood
| BASIC SEISMIC-FORCE RESISTING SYSTEM | R |
|---|---|
| A. BEARING WALL SYSTEMS | |
| Light-framed walls with shear panels: wood structural panel walls for structures | |
| three stories or less | 5.5 |
| Heavy timber braced frames where bracing carries gravity load | 2.8 |
| All other light framed walls | NA |
| B. BUILDING FRAME SYSTEMS | |
| Ordinary heavy timber-braced frames | 5.6 |
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ReplyDeletewhat is the difference between dual systems and shear wall-frame interaction systems?
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