Post on 15-Apr-2017
Design Standards for Railway Structures and Commentary
(Cut and Cover Tunnel)Ghani
Introduction
Limit state design Allowable stress method
Ultimate limit state Serviceability limit state Fatigue limit state
Safety Factor
Load factor,
Structural analysis factor,
Material factor,
Member factor, Ground investigation coeff.,
Ground resistance coeff., Structure factor,
!
Design of Main Structure
Characteristic value of load, Fk
Design load, Fd = γf . Fk
Section force, S(Fd)
Design section force, Sd = ∑{γa
.S(Fd)}
Load factor, γf
Structural analysis coeff., γa
Section Force
Characteristic value of material strength, fk
Design strength of material, fd = fk / γm
Section capacity, R(fd)
Design section capacity, Rd = R(fd) / γb
Material factor, γm
Member factor, γb
Section Capacity
Verification equation,γi . Sd / Rd < 1.0
Safety from: Bending moment, axial force,
shear force
Safety from: Floating
Must satisfy
γ1 . Us / (WS+WB.2Q2+2QB) < 1.0
Must satisfy
1. Ultimate Limit State Study of safety from section failure and body stability:
Design of Main Structure
2. Serviceability Limit State Study of stress and cracking:
(i) Stress under bending moment and axial force:
Regarding the limits on stress, the bending compressive stress of concrete during action by permanent load is 40% or less of the design compressive strength, and the tensile stress of steelduring action by variable load is equal to or less than the design tensile yield strength.
(ii) Cracking:
Design of Main Structure
3. Fatigue Limit State
In a case where the percentage variable load share of the design section force is large and the number of cycles high, safety from fatigue is studied by confirming that the conditions in equation below are satisfied.
γi . σrd /(frd / γb ) < 1.0
Design of Temporary Work
(Design Standards for Railway Structures and Commentary – Cut
and Cover Tunnel)
Surveying
Planning
Hypothesizing Design
Condition
Design START
Is it sandy soil with high
groundwater level?
Studying boilingYES
Is there artesian water
below the bottom surface
of the cut?
NO
Studying heavingYES
Is it soft clay ground?
NOStudying heaving
by background load
YES
H > 15 m
NO
NOIs it based
on customary
design method?
YES•Computing embedding depth•Studying support work and wall surface
*Customary design method
•Deciding ground constant•Hypothesizing groundwater level•Construction environment
•Setting cutting range •Soil retaining work•Support work•Cutting (excavation) method•Auxiliary work method
Selecting soil retaining wall
YES NO
Can be used as main body
Hypothesizing cutting method and sequence, support work
type and location
Computing load
Computing design embedding length
•Embedment length decided based on:• balance of moments• boiling• creeping• heaving• bearing force
ABC
Section computation of wall body
Studying struts
C
B
A
• Struts• Ground anchor• Reinforcing material
Studying wales and angle braces
Computing deformation of soil
retaining wall
Is displacement of the soil retaining wall within the
allowable value?
NO• Allowed value decided based on tie-ins with main structure• Allowed value decided based on failure of background
NO
NO
Is displacement of surrounding
structures within allowable value?
NO Allowed value based on surrounding environment conditions
ENDYES
Special comment)* This design flow chart was mainly the elastic-plastic method. For the customary designmethod, necessary items are studied as convenient
Calculation (1)Active lateral pressure
Ps = Ks.qs
qs = surcharge load (10 kN/m2)
Ks = Ka
cohesion
For sand: For clay:
Wall friction, δ = ɸ/3
Passive lateral pressure
Pp = Kpr(Σγ ti ・ hi - Pw) + Kpc ・ c + Pw in the case of sand Pp = Kpr(Σγ ti ・ hi) + Kpc ・ c in the case of clay
Σγ ti ・ hi - Pw > 0
Where:Pp: Passive lateral pressure (kN/m 2 ) Kpr: Passive lateral pressure coefficient of dead weight component of soil at the focus point Kpc: Passive lateral pressure coefficient of cohesive component of soil at the focus point c: Cohesion of soil at the focus point Σγ ti ・ hi: All of overburden pressure of soil at the focus point Pw: Pore water pressure at the focus point
𝐾 𝑝𝑟=cos𝜑2/{1−√ sin (𝜑+𝛿 ) .sin 𝜑cos𝛿 }
2
𝐾 𝑝𝑐=2√𝐾 𝑝𝑟
Calculation (2)Equal lateral pressureThe equal lateral pressure used for the beam elasto-plastic spring method is the lateral pressure that acts on the passive side as lateral pressure that does not contribute to deformation of the wall.
Accordingly, the computation is done based on the effective active lateral pressure and the effective passive lateral pressure obtained by subtracting the equal lateral pressure from the active and passive lateral pressures shown in the following Figure.
Boiling
Heaving
Heaving by background load
Embedment Length Design1. Toe stability based on lowest strut 2. Toe stability based on pivot point below excv. base
Designing Strut𝜎 𝑐
𝜎𝑐 𝑎𝑧+
𝜎 𝑏𝑐
𝜎 𝑏𝑎𝑦 ( 1−𝜎𝑐
𝜎 𝑒𝑎𝑦 )≤1
𝜎 𝑐=NA N=
𝑅×𝐵𝑛 +∆𝑁
𝜎 𝑏𝑐=𝑀𝑍 𝑀=
𝑊 0 .𝐿𝑘2
8
𝜎 𝑏𝑎𝑦=[140−2.4 (𝛽−4.5 ) ] 1.5
𝛽=𝐿𝑏
𝜎 𝑒𝑎𝑦=1100000
( 𝐿𝑟 𝑦 )2
Additional CalculationCalculation of Stress for Wale
𝑆𝑡𝑟𝑒𝑠𝑠 ,𝜎𝑏 : 𝑀𝑍 ≤ 𝜎𝑏𝑎
= Allowable bending stress
= Load to wale (kN/m/wale)
= Bending span of wale (m)
𝑊 𝑜=𝑅 . 𝛽 = Strut reaction per unit width
= Effective ratio to wale
= Section modulus (mm3)
𝜎 𝑏𝑎= {140−2.4 ( 𝜆−4.5 ) }1.5