Lecture 2 Structural System Overview CVEN Structural Concrete Design January 15, 2003

CVEN 444 Structural Concrete Design2 Presentation Overview 1. RC structural systems 2. RC structural members 3. Advantages and disadvantages of concrete structures

CVEN 444 Structural Concrete Design3 One-Way Joist Floor System 2D lateral frames Floor joists, type Rib (joist) slab : (One-way bending) 2D gravity or lateral frames

CVEN 444 Structural Concrete Design4 One-Way Joist Floor System Lateral space frame Floor joists, type Rib (joist) slab with beams: (One-way bending)

CVEN 444 Structural Concrete Design5 One-Way Joist Floor System 2’ or 3’ cc. – Joists 4’ or 6’ cc. – Skip joists 5’ or 6’ cc – Wide-module joists Top of Slab 1:12 Slope, type 8-24” for 30” Modules 16-24” for 53” Modules 14-24” for 66” Modules. Width varies 4”, 6” or larger Typical Joist

CVEN 444 Structural Concrete Design6 One-Way Joist Floor System Advantages: Longer spans with heavy loads Reduced dead load due to voids Electrical, mechanical etc. can be placed between voids Good vibration resistance Typical Applications: Medium-to-long spans with heavy loading For 30” modules, 35’ – 40’ spans For 53” & 66” modules, 35’ – 50’ spans

CVEN 444 Structural Concrete Design7 Two-Way Joist Floor System 2D lateral frames Waffle pans, type Waffle slab : (Two-way bending)

CVEN 444 Structural Concrete Design8 Two-Way Joist Floor System Advantages: Longer spans with heavy loads Reduced dead load due to voids Electrical, mechanical etc. can be placed in voids Good vibration resistance Attractive Ceiling Typical Applications: Long spans with heavy loading For 3’, 4’, and 5’ modules, 40’ – 50’ spans and beyond

CVEN 444 Structural Concrete Design9 Floor System Effective Cost (PCA 2000) Bay Spacing, ft Live Load, psf One-way joistFlat SlabFlat Plate

CVEN 444 Structural Concrete Design10 B. Lateral Load Systems Frame Overview Flat plate (& slab)-column (w/ and w/o drop panels and/or capitals) frame systems Beam-column frame systems Shear wall systems (building frame and bearing wall) Dual systems (frames and shear walls)

CVEN 444 Structural Concrete Design11 Frame: Coplanar system of beam (or slab) and column elements dominated by flexural deformation Planar (2D)Space (3D)

CVEN 444 Structural Concrete Design12 Basic Behavior Gravity LoadLateral Loading

CVEN 444 Structural Concrete Design13 2D vs. 3D Frames (Plan) PlanarSpace Floor joists, type 2 or 4 frames, 2 frames4 frames, 4 frames

CVEN 444 Structural Concrete Design14 Frame Advantages Optimum use of floor space, ie. optimal for office buildings, retail, parking structures where open space is required. Relatively simple and experienced construction process Generally economical for low-to mid-rise construction (less than about 20 stories) In Houston, most frames are made of reinforced concrete.

CVEN 444 Structural Concrete Design15 Frame Disadvantages Generally, frames are flexible structures and lateral deflections generally control the design process for buildings with greater than about 4 stories. Note that concrete frames are about 8 times stiffer than steel frames of the same strength. Span lengths are limited when using normal reinforced concrete (generally less than about 40 ft, but up to about 50 ft). Span lengths can be increased by using pre-stressed concrete.

CVEN 444 Structural Concrete Design16 Frame Lateral Load Systems Flat plate-column frame: Plan Elevation Effective slab width

CVEN 444 Structural Concrete Design17 Frame Lateral Load Systems Beam-column frame: Elevation

CVEN 444 Structural Concrete Design18 Frame Lateral Load Systems Diaphragm (shear) element: Carries lateral loading to the lateral load resisting system Lateral load frame, type. Plate element Deformed shape - Lateral load distributes to frames proportional to tributary area

CVEN 444 Structural Concrete Design19 Frame Lateral Load Systems For relatively square plans, diaphragms are generally considered rigid Space frame with square plan Deformed shape has constant lateral displacement - No diaphragm flexibility, ie. lateral load distributes to frame proportional to frame stiffness

CVEN 444 Structural Concrete Design20 Shear Wall Lateral Load Systems Shear wall Elevation Edge column Interior gravity frames Shear deformations generally govern

CVEN 444 Structural Concrete Design21 Shear Wall Lateral Load Systems Gravity frames Shear walls Coupling beams Elevator shaft configuration Hole

CVEN 444 Structural Concrete Design22 Dual Lateral Load Systems Lateral frames – 25% of lateral load, minimum Shear walls Wall-Frame Dual System: Hole

CVEN 444 Structural Concrete Design23 4. Structural Members Beams Columns Slabs/plates/shells/folded plates Walls/diaphragms

CVEN 444 Structural Concrete Design24 Beam Elements Defn: Members subject to bending and shear Elastic Properties: k b = f ( EI/L n ) (bending)  = My/I (normal stress) k s = GA/L (shear)v = VQ/Ib (shear stress)  b = f (load, support conditions, L, E, I) (bending) V VL E,I,A MM        

CVEN 444 Structural Concrete Design25 Column Elements Defn: Members subject to bending, shear, and axial Elastic Properties: k a = EA/L (axial)  a = F/A (normal stress) k b = f ( EI/L n ) (bending)  b = My/I (normal stress) k s = GA/L (shear)v = VQ/Ib (shear stress)  b = f (load, support conditions, L, E, I, A) (normal) V VL E,I,A MM FF         

CVEN 444 Structural Concrete Design26 Slab/Plate Elements Defn: Members subject to bi-directional bending & shear x y z M x, M y, and V z  x,  y, and  z

CVEN 444 Structural Concrete Design27 Wall/Diaphragm Elements Defn: Members subject to shear x y V x and V x  x and  y

CVEN 444 Structural Concrete Design28 Advantages of Concrete Structures Economical Thinner floor systems Reduced Building Height Lower wind loads (< A) Saving in Cladding Materials widely available

CVEN 444 Structural Concrete Design29 Advantages of Concrete Structures Suitability of material for architectural and structural function Concrete place in plastic condition - desired shape & texture can be obtained with forms and finishing techniques Designer can choose shape and size

CVEN 444 Structural Concrete Design30 Advantages of Concrete Structures Fire Resistance Concrete building have 1-3 hour fire rating with no fire proofing (steel and timber require fireproofing to obtain this rating) Rigidity Greater stiffness & mass reduces oscillations (wind), floor vibrations (walking)

CVEN 444 Structural Concrete Design31 Advantages of Concrete Structures Low Maintenance Availability of Materials Sand, gravel, cement, H 2 0 & concrete mixing facilities widely available Reinforcement - easy to transport as compared to structural steel

CVEN 444 Structural Concrete Design32 Disadvantages of Concrete Structures Low tensile strength - ~ 0.1 f c cracking if not properly reinforced

CVEN 444 Structural Concrete Design33 Disadvantages of Concrete Structures Forms and Shoring (additional steps) Construction of forms Removal of forms Prepping (or shoring) the new concrete to support weight until strength is adequate. Labor/Materials cost not required for other types of materials

CVEN 444 Structural Concrete Design34 Disadvantages of Concrete Structures Strength per unit volume is relatively low. f c ~ (5-10% of steel) greater volume required long spans typical built with steel

CVEN 444 Structural Concrete Design35 Disadvantages of Concrete Structures Time-dependent volume changes Concrete & steel undergo similar expansion and contraction. Concrete undergoes drying shrinkage, which may cause deflections and cracking. Creep of concrete under sustained loads causes an increase in deflection with time.