Programa de Agua Segura para Lima y Callao - PASLC

4.2.1 General Description and Geometrical Configuration

Nine prototype buildings, representative of the range of mid-rise building stock in Egypt, are selected to generate the displacement relations needed for application of the HFD method for RC structures. The buildings are assumed to have a constant floor height of 3.0 m and bay width of 6.0 m, with the number of floors and bays being varied as 4, 7 and 10 floors, and 3, 5 and 7 bays, respectively. The structural system chosen is moment-resisting frames (MRFs) since it reflects the type of concrete construction commonly used in Egypt, and as its design is generally more controlled by drift

Chapter 4

limitations than shear wall systems or combined systems, and as discussed earlier, drift ratio is the response of interest in the proposed method. Office use and symmetrical square layouts are assumed to maintain generality in the developed findings. The prototype buildings’ configurations and notations are summarized in Table 4-1, and their elevations are presented in Figure 4-1.

Table 4-1 Prototype Buildings’ description and notation

Structure reference Number of stories Number of bays

F04B3 4 3 F04B5 4 5 F04B7 4 7 F07B3 7 3 F07B5 7 5 F07B7 7 7 F10B3 10 3 F10B5 10 5 F10B7 10 7

Chapter 4

4.2.2 Design Details and Assumptions

The buildings are designed and detailed to resist combination of gravity and seismic loads, according to the Egyptian Code of Practice ECP-203 (2007), and ECP- 201 (2012), which is fundamentally in line with the regulations of Eurocode 8 (EN 1998-1, 2004), a typical modern seismic code applicable to many countries with different seismicity, soil conditions, and construction practice. The buildings are assumed to reside in the highest seismic zone in Egypt (Zone 5B), with a peak ground acceleration (PGA) of 0.3g. The reason for the selection of this design peak ground acceleration, despite Zone 5B just covering secluded areas of the country, is to provide some generality in the results. This value would correspond to merely a medium seismic hazard in other highly seismic locations in the world like California in the United States Also, choosing this high seismicity serves to magnify the seismic effects in order to attain significant difference between nonlinear and linear behavior.

For gravity loading, the considered dead load comprises the self-weight of the concrete structural elements, a typical floor finishing of 1.5 kN/m2, and weight of masonry infill panels of 120- and 250-mm thickness on interior and exterior beams, respectively with a density of 18 kN/m3. A live load of 3.0 kN/m2 is also included. For seismic design, the lateral load resisting system is chosen as a space frame. The acceleration elastic response spectrum for shallow crustal earthquakes in non- Mediterranean areas is adopted known as Type 1 in ECP-201 (2012), and as Type 2 in EC8 (EN1998-1, 2004), for a "Soil Class C" which is soft soil, or dense or medium- dense sand, gravel or stiff clay as given in ECP-201(2012) and EC8 (EN1998-1, 2004). The design spectrum is scaled by an “Importance factor” of 1.2 to reflect the added conservatism for public office buildings. Based on the norm and know-how of reinforcement detailing in Egypt and many other countries with similar low-to- moderate seismicity, limited ductility frames are chosen and thus, a FRF with a value of 5 is used in the design. Characteristic material properties are utilized, and they are presented in Table 4-2 using units consistent with those that will be used in the program for nonlinear time-history analysis, as noted in Section 4.3.2.4.

Chapter 4

Gravity and seismic loading are combined using the appropriate coefficients from ECP-203 (2007), so the buildings are designed to satisfy both of the following code’s combinations: U1 = 1.4D + 1.6L ……….….(4.1) U2 = 1.12D + αL + S ………...(4.2) Where U : ultimate load D: dead load L : live load S : Seismic load

α: live load factor representing the live load percentage existing during earthquakes and taken as 0.5 for public and office buildings.

The only capacity design rule applied is that resulting from the prescribed reduction in effective flexural stiffness of members where the stiffness reduction for beams (50%) is higher than that for columns (30%). All floors are assumed to have a solid rigid slab with a constant thickness of 150 mm, and columns are selected to have a square cross-section and to be symmetrically reinforced on the four sides, in order to have equal resistance to the changing direction of earthquake loading. The reinforcement is selected minimally according to the structural analysis and code requirements, to avoid overstrength and unnecessary margins reflecting personal designers’ choices. Member cross-section sizes and reinforcements are summarized in Table 4-3,

Table 4-2 Properties of materials employed in design and time-history analysis

Material parameter Values used

C

oncre

te 28d compressive cube strength, fcu 25 N/mm2

Modulus of elasticity, Ec 22 kN/mm2 Poisson’s ratio 0.2 Ste el (36/ 5 2) Yield strength, Fy 360 N/mm2 Ultimate strength, Fu 520 N/mm2 Modulus of elasticity, Es 206 kN/mm2

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Table 4-3 Member dimensions and reinforcement of the prototype frames

Building Floor #

Outer Columns Inner Columns Beams (width =250mm) Size (mm) Rein- forcement Size (mm) Rein- forcement Depth (mm) Top Rein- forcement Bottom Rein- forcement 4-story 1-4 450 8 22 600 16 20 750 8 18 4 18 7-story 1-4 550 12 20 650 16 22 750 7 20 3 20 5-7 450 8 22 450 8 22 650 7 18 5 16 10-story 1-4 650 20 22 750 20 22 750 7 20 3 20 5-7 550 12 22 650 16 22 650 6 20 3 20 8-10 450 8 22 400 8 20 600 7 16 3 18

The following are the assumptions considered in this design stage:

1. Floor diaphragms are sufficiently rigid relative to the lateral force resisting system, so they distribute the seismic load among the MRFs without significant deformation.

2. A change in sections of beams and columns every three stories has been adopted as a representative choice of concrete design practice.

3. Due to symmetry, only MRFs in the X-direction are studied and vertical accelerations are ignored.

4. Columns are designed for combinations of axial compression and moments due to the framing action, using the interaction diagrams.

5. Beam-column joint shear deformations are neglected.

6. Only torsion due to accidental eccentricity is considered due to symmetry. 7. Combined shear and torsion effect is neglected.

8. Lateral loads due to wind are not considered in the design.

9. Masses are distributed on structural elements following the dead load distribution. 10. Non-structural elements are fixed so as not to interfere with structural response. 11. No-second order effects (P-delta effects) are taken into consideration at the design

stage (however they are considered in the nonlinear time history analysis presented in the sequel)

Chapter 4