STRC04_PrestressedConcrete_0116
March 23, 2017 | Author: Kevin | Category: N/A
Short Description
PPI2PASS SE Exam Review Course Lecture 04 Structural Engineering Course...
Description
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design Structural Engineering Review Course
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
1
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Lesson Overview Prestressed Concrete Design • Design Stages • Design for Shear • Design for Torsion • Prestress Losses • Composite Construction • Load Balancing Procedure
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
2
2
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Learning Objectives You will learn • prestressed concrete design • how to avoid pitfalls on the SE exam • tricks to speed up problem solving
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
3
3
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Prerequisite Knowledge You should already be familiar with • statics • mechanics of materials • structural analysis • basic reinforced concrete design • basic prestressed concrete terminology
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
4
4
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Referenced Codes and Standards • International Building Code (IBC, 2012) • Building Code Requirements for Structural Concrete (ACI 318, 2011) • PCI Design Handbook: Precast and Prestressed Concrete (PCI, 2010)
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
5
5
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Design Stages: General Requirements transfer design stage • losses to consider
•
forces to consider
• elastic shortening
•
prestressing force
• friction (post‐tensioned only)
•
self‐weight of the member
• anchor seating (post‐tensioned only)
• Check stresses due to service loads against the allowable values.
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
6
6
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Design Stages: General Requirements serviceability design stage • additional losses to consider
• additional forces to consider
• creep
• remainder of dead load
• shrinkage
• live load
• relaxation
• Check stresses due to service loads against the allowable values.
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
7
7
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Design Stages: General Requirements strength design stage • factored loads • Check design strength against required strength. • Assume rectangular stress block with maximum concrete strain of 0.003. Fig. 1.1 Rectangular Stress Block
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
8
8
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Poll Question When analyzing a pretensioned beam at the serviceability design stage, how many different types of losses need to be considered? (A) 0 (B) 3 (C) 4 (D) 6
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
9
9
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Poll Question When analyzing a pretensioned beam at the serviceability design stage, how many different types of losses need to be considered? (A) 0 (B) 3 (C) 4 (D) 6 The answer is (C). Check all losses except for anchorage and friction (which apply to post‐tensioned members only). The four losses are elastic shortening, creep, shrinkage, and relaxation. STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
10
10
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Design Stages: Transfer Design Stage initial prestressing force mobilizes self‐ weight of member, producing stresses
Fig. 3.1 Transfer Design Stage
• top fiber stress
• bottom fiber stress
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
11
11
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Design Stages: Transfer Design Stage permissible stresses
Fig. 3.2 Specified Concrete Stress at Transfer
• in concrete, as shown in Fig. 3.2 • at post‐tensioning anchorage • due to tendon jacking force f ci'
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
12
12
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Design Stages: Transfer Design Stage permissible stresses (continued)
Fig. 3.3 Specified Stress in Prestressing Tendons
in tendon, as shown in Fig. 3.3
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
13
13
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Design Stages auxiliary reinforcement • When calculated tensile stress exceeds permissible stress, provide bonded auxiliary reinforcement to resist the total tensile force in the concrete. • tensile force based on uncracked properties • permissible stress is 0.6fy
30 ksi
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
14
14
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Design Stages auxiliary reinforcement (continued)
Fig. 3.4 Determination of Tensile Force
• depth of zero stress
• tensile force
• required auxiliary reinforcement
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
15
15
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Design Stages: Serviceability Design Stage stress condition as shown in Fig. 3.5 • top fiber stress • bottom fiber stress Fig. 3.5 Serviceability Design Stage After all Losses
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
16
16
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Design Stages: Serviceability Design Stage member type class U
class T
• Use uncracked section properties for stress calculation.
• Use uncracked sections properties for stress calculation.
• No crack control measures required.
• No crack control measures required.
• Deflections are based on uncracked section properties.
• Deflections are based on cracked transformed section properties.
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
17
17
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Design Stages: Serviceability Design Stage member type (continued)
Fig. 3.6 Permissible Concrete Stress at Service Load
class C • use cracked section properties for stress calculation • crack control measures per ACI Sec. 10.6.4, Sec. 10.6.7, and Sec. 18.4.4.1 • deflections based on cracked transformed section properties permissible stresses shown in Fig. 3.6 STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
18
18
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Design Stages cracking moment • modulus of rupture
ACI Eq. 9‐10
• cracking moment • flexural strength Mn 1.2Mcr waived for members with shear and flexural design strength 2 required strength Fig. 3.7 Cracking Moment
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
19
19
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Example: Design Stages CSCO Example 10.1
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
20
20
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Example: Design Stages
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
21
21
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Example: Design Stages
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
22
22
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Example: Design Stages
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
23
23
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Example: Design Stages A 30 ft long, simply supported beam made of normal weight concrete has the given values. Most nearly, what is the cracking moment strength? Ag = 300 in2
MD = 0.5 kip-ft
Aps = 0.75 in2
St = 1200 in3
ML = 0.2 kip-ft
e = 8 in
Sb = 1400 in3
Pe = 112 kips
fse = 150 ksi
Rt = −0.00238 1/in2
Pi = 150 kips
fc’ = 6 ksi fci’ = 4 ksi
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
24
24
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Example: Design Stages 7.5
1
7.5 1.0
1 300 in
6000
580
8 in 1400 in3 1400 in2
0.580
0.00905 1/in kips 112 2 in
0.00905
1 in2
0.580
kips in
1 in 12 ft
186 ft‐kips
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
25
25
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Design Stages strength design stage
Fig. 3.8 Strain Distribution and Internal Forces at Flexural Failure
• nonprestressed reinforcement assumed to contribute to ultimate moment of resistance • •
•
STRC ©2015 Professional Publications, Inc.
© 2016 Professional Publications, Inc.
26
26
Structural Engineering Review Course
Prestressed Concrete Design
Prestressed Concrete Design
Design Stages strength design stage (continued)
Fig. 3.9 Strain Distribution at Nominal Strength
tension and compression‐controlled section Calculate strain. Then, • for
t
0.005, = 0.90
• for
t
0.002, = 0.65
• for 0.002
View more...
Comments
