twenty five http:// nisee.berkeley.edu/godden concrete - PowerPoint PPT Presentation

A RCHITECTURAL S TRUCTURES : Reinforced Concrete Design F ORM, B EHAVIOR, AND D ESIGN ARCH 331 • economical & common D R. A NNE N ICHOLS • resist lateral loads S PRING 2019 lecture twenty five http:// nisee.berkeley.edu/godden concrete construction: flat spanning systems Concrete Spans 1 Architectural Structures F2009abn Concrete Spans 2 Foundations Structures F2008abn Lecture 25 ARCH 331 Lecture 25 ARCH 331 Reinforced Concrete Design Reinforced Concrete Design • beam supported • flat plate – slab depth ~ L/20 – 5 ” -10 ” thick – 8 ”– 60 ” deep – simple formwork – lower story heights • one-way joists The Architect ’ s Studio Companion • flat slab – 3 ”– 5 ” slab – 8 ”– 20 ” stems – same as plate – 5 ” -7 ” webs – 2 ¼”– 8 ” drop panels Concrete Spans 4 Foundations Structures F2008abn Concrete Spans 3 Foundations Structures F2008abn Lecture 25 ARCH 331 Lecture 25 ARCH 331 1

Reinforced Concrete Design Reinforced Concrete Design • two-way joist • simplified frame analysis – “ waffle slab ” – strips, like – 3 ” -5 ” slab continuous beams • moments require – 8 ” -24 ” stems flexural reinforcement – 6 ” -8 ” webs – top & bottom • beam supported slab – both directions of slab – 5 ” -10 ” slabs – continuous, bent or – taller story heights discontinuous Concrete Spans 5 Foundations Structures F2008abn Concrete Spans 6 Foundations Structures F2008abn Lecture 25 ARCH 331 Lecture 25 ARCH 331 Reinforced Concrete Design Reinforced Concrete Design • one-way slabs (wide beam design) – approximate analysis for moment & shear coefficients – two or more spans – ~ same lengths – w u from combos – uniform loads with L/D  3 –  n is clear span (+M) or average of adjacent clear spans (-M) Concrete Spans 7 Foundations Structures F2008abn Concrete Spans 8 Foundations Structures F2008abn Lecture 25 ARCH 331 Lecture 25 ARCH 331 2

Reinforced Concrete Design Reinforced Concrete Design • two-way slabs - Direct Design Method – 3 or more spans each way – uniform loads with L/D  2 – rectangular panels with long/short span  2 – successive spans can’t differ > longer/3 – column offset no more than 10% span Concrete Spans 9 Architectural Structures F2008abn Lecture 25 ARCH 331 Concrete Spans 10 Foundations Structures F2008abn Lecture 25 ARCH 331 Shear in Concrete Shear in Concrete • at columns • critical section at d/2 from • want to avoid – column face, column capital or drop panel stirrups • can use shear studs or heads Concrete Spans 11 Foundations Structures F2008abn Concrete Spans 12 Foundations Structures F2008abn Lecture 25 ARCH 331 Lecture 25 ARCH 331 3

Shear in Concrete Openings in Slabs • at columns with waffle slabs • careful placement of holes • shear strength reduced • bending & deflection can increase http:// nisee.berkeley.edu/godden Concrete Spans 13 Foundations Structures F2008abn Concrete Spans 14 Foundations Structures F2008abn Lecture 25 ARCH 331 Lecture 25 ARCH 331 General Beam Design (cont ’ d) General Beam Design • f ’ c & f y needed • custom design: • usually size just b & h – longitudinal steel – shear reinforcement – even inches typical (forms) – detailing – similar joist to beam depth – b:h of 1:1.5-1:2.5 – b w & b f for T – to fit reinforcement + stirrups 2 bh S  • slab design, t 6 – deflection control & shear Concrete Spans 15 Foundations Structures F2008abn Concrete Spans 16 Foundations Structures F2008abn Lecture 25 ARCH 331 Lecture 25 ARCH 331 4

Space “ Frame ” Behavior Space “ Frame ” Behavior • handle uniformly distributed loads well • shear at columns • bending moment • support conditions still important – tension & – point supports not optimal compression • fabrication/construction can dominate “ couple ” with design depth – member sizes can vary, but difficult Concrete Spans 17 Foundations Structures F2008abn Concrete Spans 18 Foundations Structures F2008abn Lecture 25 ARCH 331 Lecture 25 ARCH 331 Folded Plates Folded Plates • increased bending stiffness with folding • common for roofs • edges need • lateral buckling avoided stiffening http:// nisee.berkeley.edu/godden Concrete Spans 20 Foundations Structures F2008abn Concrete Spans 19 Foundations Structures F2008abn Lecture 25 ARCH 331 Lecture 25 ARCH 331 5

Folded Plates www.library.illinois.edu – State Farm Center (Assembly Hall), University of Illinois – Harrison & Abramovitz 1963 – Edge-supported dome spanning 400 feet wound with 614 miles of one-fifth inch steel wire Concrete Spans 21 Foundations Structures F2008abn Lecture 25 ARCH 331 6