s5 Ec8-Lisbon m Fardis
-
Upload
carlos-costa -
Category
Documents
-
view
238 -
download
0
Transcript of s5 Ec8-Lisbon m Fardis
-
7/21/2019 s5 Ec8-Lisbon m Fardis
1/28
Dissemination of information for training Lisbon 10-11 February 2011 1
Design and detailing ofsecon ary se sm c e emen s
Provisions for concrete dia hra ms
M.N. FardisUniversity of Patras (GR)
-
7/21/2019 s5 Ec8-Lisbon m Fardis
2/28
Dissemination of information for training Lisbon 10-11 February 2011 2
MASONRY-INFILLED FRAMES
-
7/21/2019 s5 Ec8-Lisbon m Fardis
3/28
Overall effect of masonry infil ls on seismic performance
Dissemination of information for training Lisbon 10-11 February 2011 3
Field experience & numerical/experimental research do show
that: masonry infills attached to the structural frame, in general have a
beneficial effect on seismic erformance es eciall if the buildin
structure has little engineered earthquake resistance.
,
distributed infill panels: reduce, through their in-plane shear stiffness, storey drift demands &
deformations in structural members
increase, via their in-plane shear strength, storey lateral force resistance,
contribute, throu h their h steresis, to the lobal ener dissi ation.
In buildings designed for earthquake resistance, non-structural
significant overstrength.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
4/28
Position of EC8 on masonry infi lls
Dissemination of information for training Lisbon 10-11 February 2011 4
Eurocode 8 does not encourage designers to profit from
the beneficial effects of masonry infills to reduce the
seismic action effects for which the structure is designed.
Eurocode 8 warns against the adverse effects of infills &
.
& the surrounding frame (by shear connectors, or other
as a confined masonry building, not as a concrete
structure with masonr infills.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
5/28
Possible adverse effects of masonry infil ls
Dissemination of information for training Lisbon 10-11 February 2011 5
Infills that are too strong & stiff relative to the concrete
structure itself
may override its seismic design, including thee or s o e es gner e n en o o con ro
inelastic response by spreading inelastic
(e.g. when ground storey infills fail soft storey).
Infills non-uniformly distributed in plan or in elevation:
part of the structure.
Adverse local effects on structural frame pre-emptive brittle failures.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
6/28
Possible adverse effects of masonry infills (contd)
Dissemination of information for training Lisbon 10-11 February 2011 6
Best way to protect concrete building from adverse
effects of irregular masonry infilling:
shear walls sufficiently strong/stiff to overshadow anye ec s o e n ng.
Shear walls that resist at least 50% of the seismic base
-
for waiving the special requirements for buildings with
-
7/21/2019 s5 Ec8-Lisbon m Fardis
7/28
Possible adverse effects of masonry infills (contd)
Dissemination of information for training Lisbon 10-11 February 2011 7
Worst possible effect: Open ground storey soft-storey
~02 (c)
infill strut
1
2-storey frame: Elements in infilled storey shielded from large moments &
deformations. But round store columns are overloaded. See:
(a) bending moments & deformation in frame w/o infills;(b), (c) bending moments & deformation in frame w/ stiff infills in 2nd storey.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
8/28
Open ground storey
Dissemination of information for training Lisbon 10-11 February 2011 8
Collapse of ground storey due to reduction of
infills:
(a) Olive View Hospital, San Fernando, Ca, 1971;(b) Aegio (GR) 1995
(b)
Collapse of ground storey due to reduction of infills:(a) Olive View Hospital, San Fernando, Ca, 1971; (b) Aegio (GR) 1995
a
-
7/21/2019 s5 Ec8-Lisbon m Fardis
9/28
EC8 design for infi ll irregularity in elevation
Dissemination of information for training Lisbon 10-11 February 2011 9
Eurocode 8: Design columns of storey where infills are reduced
re a ve o over y ng s orey, o rema n e as c n s n s orey a ove
reach their ultimate force resistance:
Deficit in infill shear stren th in a store is com ensated b an
increase in resistance of the frames (vertical) members there:
In DC H frame or frame-equivalent dual buildings, seismic M, V, N in
multiplied by: qVV EdRw /1
VRw: total reduction of resistance of masonry walls in storey
concerned w.r.to storey above,
Ed
seismic members of the storey (storey design shear).
If < 1.1: magnification of seismic action effects may be omitted.
Although not required for DC M frame or frame-equivalent dual
buildings, the above are (weakly) recommended for them as well.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
10/28
Asymmetry of infills in plan
Dissemination of information for training Lisbon 10-11 February 2011 10
Asymmetric distribution of infills in plan torsional
response to translational horizontal components of
seismic action: em ers on e s e w e ewer n s ex e s e
are subjected to larger deformation demands & fail first.
The increase in global lateral strength & stiffness due to
interstorey drift demands in plan:
The maximum member deformation demands for planwiseirregular infilling do not exceed peak demands anywhere
in plan, in a similar structure w/o infills.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
11/28
EC8 design against infill planwise asymmetry
Dissemination of information for training Lisbon 10-11 February 2011 11
Eurocode 8: doubles accidental eccentricity (from 5 to 10%) in
the analysis, if the infills are planwise irregular.
Doubling of accidental eccentricity: is not enough for severely
irregular arrangement of infills in plan , Need sensitivity analysis of the effect of stiffness & position of infills
(disregarding one out of 3-4 infill panels per planar frame, especially on the
ex e s es .
In-plane modelling of infills. Simplest modelling of solid panel (without openings):
Two diagonal struts.
Effect of openings: Reduction factors?
The above are required for DC H frame
or rame-equ va en ua u ngs an
(weakly) recommended for DC M ones.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
12/28
Adverse local effects on structural frame
Dissemination of information for training Lisbon 10-11 February 2011 12
Shear failure of weak
columns due to interaction
-
7/21/2019 s5 Ec8-Lisbon m Fardis
13/28
EC8 design against local effect of strong infills
Dissemination of information for training Lisbon 10-11 February 2011 13
Shear loading of the column by the infill strut force:
Eurocode 8 for all columns: verify in shear a length lc=winf/cos, near the top &
e o om o e co umn over w c e agona s ru orce o n may e
applied, for the smaller of the two design shear forces:
The horizontal component of the infill strut force, taken equal to thehorizontal shear strength of the panel (shear strength of the bed joints times
the horizontal cross-sectional area of panel); or
Capacity design shear: 2 M (: design value of column moment resistance),
/ lc(: contact length) Width of the strut (e.g.):
4.0inf
cos
.
Hw n
1
4
ncc
ww
HIE
uroco e : rac on ~ o pane agona , bn cos
Columns in contact with infill all along only one side: Full clear height = criticalregion
-
7/21/2019 s5 Ec8-Lisbon m Fardis
14/28
Adverse local effects on structural frame (contd)
Dissemination of information for training Lisbon 10-11 February 2011 14
Shear failures of short (captive) columns
-
7/21/2019 s5 Ec8-Lisbon m Fardis
15/28
EC8 design of squat captive columns
Dissemination of information for training Lisbon 10-11 February 2011 15
Capacity-design calculation of design shear force, w/: clear len th of the column, l = len th of the column not in contact to the
infills &
plastic hinging assumed to take place at the column section at the
.
Transverse reinforcement required to resist the design
shear force is placed not just along the clear length of the
column, lcl, but also into the column part which is incontact to the infills (over length equal to the column
depth, hc, within plane of infill).
Entire length of the column is taken as critical region, withs rrups e a e as n co umn cr ca reg ons.
Use diagonal reinforcement over length of column not in
, .
times the column depth.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
16/28
Dissemination of information for training Lisbon 10-11 February 2011 16
SECONDARY SEISMIC ELEMENTS IN
EC8
-
7/21/2019 s5 Ec8-Lisbon m Fardis
17/28
Secondary seismic elements
Dissemination of information for training Lisbon 10-11 February 2011 17
Contribution of secondary seismic elements to resistance & stiffness forseismic actions is discounted in design (& in linear analysis model, too).
The designer is free to assign elements to this class of elements,if:
Their total contribution to lateral stiffness 15% of that of the other rimar seismic elements
The buildings regularity classification does not change.
Secondary seismic elements:
not subject to the geometric etc. restrictions of EC8
not ULS-designed for any seismic force demands,
, .
But: they are required to remain elastic under the deformations imposed by
the design seismic action (: qtimes their deformations from an elasticana ys s w e con r u on o secon ary e emen s neg ec e :
Requirement hard to meet.
Therefore consider as secondar seismic onl those elements which
cannot be made to meet EC8 rules (e.g., if they are outside EC8s scope:prestressed girders, flat-slab frames, etc.)
-
7/21/2019 s5 Ec8-Lisbon m Fardis
18/28
Design procedure if some elements are Secondary seismic
Dissemination of information for training Lisbon 10-11 February 2011 18
1. Carry out linear analysis for the design seismic action using two models :
Model SP: including the contribution of all elements (secondary orprimary seismic) to lateral stiffness;
Model P: neglecting the contribution of secondary seismic elements
(e.g., introduce appropriate hinges at their connections to primary elements,
so that the secondary ones have stiffness only against gravity loads).
.
check that it is 115% at every storey.
3. Estimate the deformations of secondary seismic elements under the
design seismic action as qtimes their deformations from Model SP, times
the P/SP-ratio of interstorey drifts in 2 above.
secondary seismic element (50% of uncracked gross stiffness) find their
internal forces and check that they are in the elastic domain.
forces from Model SP, times q, times the P/SP-ratio of interstorey drifts from 2above.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
19/28
7-storey wall building with f lat-slab frames taken as secondary
seismicDissemination of information for training Lisbon 10-11 February 2011 19
-
7/21/2019 s5 Ec8-Lisbon m Fardis
20/28
Contribution of secondary elements to lateral stiffness 15% of that
of primary elementsDissemination of information for training Lisbon 10-11 February 2011 20
- ,of the diaphragm and taking the flat slab as an effective beam w/ width of
2.5m at the interior of the plan or 1.25m at the perimeter:
Total contribution of flat slab frames and of the walls in their weakdirection to lateral stiffness: 13.9% of that of the walls in their strong
rec on.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
21/28
Deformation-induced seismic action effects in secondary seismic
columnsDissemination of information for training Lisbon 10-11 February 2011 21
Elastic M & V in the secondary columns from elastic analysis
under design seismic action, multiplied by q and divided by
the fraction of the base shear taken by the primary seismicelements, i.e., multiplied times:
q - . = . :
V=139kN,
End moments: 240kNm and 127kNm at top & bottom.
Maximum M in any interior column:
m, a e groun s orey.
(V=141kN, at the ground storey).
-
7/21/2019 s5 Ec8-Lisbon m Fardis
22/28
Check of secondary seismic columns for the deformation-
induced seismic momentsDissemination of information for training Lisbon 10-11 February 2011 22
. . . - . .
Top storey axial loadN=205kN, givingMRdc,n=346kNm>MEc,n.
Ground storeyN=1435kN,MRdc,1=795kNm>>MEc,1.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
23/28
Check of secondary seismic columns for the deformation-induced
seismic shearsDissemination of information for training Lisbon 10-11 February 2011 23
Max. tie spacing per EC2:Max. tie spacing per EC2:
- w . bL c c - .
8mm-dia. perimeter hoop and diamond-shaped ties mid-side vertical bars, @
165mm centres:
- w . bL c c - .
8mm-dia. perimeter hoop and diamond-shaped ties mid-side vertical bars, @
165mm centres:w= + x . x = . .
Shear resistance for shear compression per EC2:VRd,max=0.3x(1-35/250)x0.6x0.9x0.565x(35000/1.5)sin2=1269kN>VEc,1,
w= + x . x = . .
Shear resistance for shear compression per EC2:VRd,max=0.3x(1-35/250)x0.6x0.9x0.565x(35000/1.5)sin2=1269kN>>VEc,1,
if cot=2.5 Shear resistance due to the ties per EC2:V =b z f cot+N h-x/H , with neutral axis de th, x= d, at the
if cot=2.5 Shear resistance due to the ties per EC2:V =b z f cot+N h-x/H , with neutral axis de th, x= d, at the,
moment resistance of the column.
- Top storey:
- = + -
,
moment resistance of the column.
- Top storey:
- = + -,s . . . . . . .0.084x0.565)/2.65 = 616.5kN>VEc,n.
- Ground storey:
,s . . . . . . .0.084x0.565)/2.65 = 616.5kN>>VEc,n.
- Ground storey:
- Rd,s . . . . . . . -
0.249x0.565)/2.65 =822.5kN>VEc,1.
- Rd,s . . . . . . . -
0.249x0.565)/2.65 =822.5kN>>VEc,1.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
24/28
Concrete diaphragms
Dissemination of information for training Lisbon 10-11 February 2011 24
ULS verification of RC diaphragms in DCH buildings: For irregular geometry or divided shapes of diaphragm in
plan, recesses or re-entrances;
If irregular distribution of masses and/or stiffnesses (set-
-
In basements with walls only in part of the perimeter or onlyin part of the ground floor area;
At the interface with core and walls in core or wall structural
systems.
o e suc ap ragms as eep eam or p ane russor strut-and-tie model, on elastic supports.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
25/28
Strut-and-Tie model of diaphragm for check of top floor slab
Dissemination of information for training Lisbon 10-11 February 2011 25
Deep beam comprising:
a Tension chord centred alonline 1 (width =lw of walls W1)
b Semi-circular compressionchord connecting ends oftension chord, apex nearcentre of orthogonal wall W2on line 2;
c ose y space tens on t esparallel to horiz. componentseismic action, running from
opposite to line 2, to collectthe in-plane loadqE=1.728kN/m
2 of top floordue to design seismic action
and transfer it to compressionchord.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
26/28
Verification of tension ties (contd)
Dissemination of information for training Lisbon 10-11 February 2011 26
Longest tension ties collect in-plane loadqE =1.728kN/m2 along the full
, x. ,section through the flat slab normal to hor. direction X should havereinforcement area at least
dq
EL
x/f
yd=1.1x1.728x25/(0.5/1.15)=110mm2/m
the moment due to the quasi-permanent floor gravity load,Mg+2q.
(d=1.1: overstrength factor per EC8 for the design of diaphragms).
The reinforcement of the flat slab has been dimensioned for ULS inbending for the flat slab moments under the factored gravity loads, Md.
e surp us o re n orcemen area over an a ove w a s necessary orULS resistance under Md: As=max[As,min; Md/(zfyd)]-Mg+2q/(zfyd), where
z=0.11m the internal lever arm, Mg+2q= (8.2/14.7)Md andAs,min them n mum re n orcemen area n e a s a per .
Critical location forAs: whereMd is minimum.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
27/28
Verif ication of tension ties
Dissemination of information for training Lisbon 10-11 February 2011 27
MinimumMd along longest tension ties:
Sagging moment at mid-distance between W2 and 1st row of interior columns
parallel to W2 (Section 1-1)
= - = 2 < 2. . . . . . . .
Increase reinforcement of flat slab within its middle strips between W2 and
the 1
st
parallel row of interior columns, and between any rows of interiorco umns, o + x . . = mm m.
Potentially critical: tension ties heading towards the edge column next to W2
Section 2-2 :A = 1-8.2/14.7 x47.3/ 0.11x0.5/1.15 =438mm2/m >110mm2/m
Between edge columns and 1st
parallel row of interior columns (Section 3-3):As=(1-8.2/14.7)x37.85/(0.11x0.5/1.15)=350mm
2/m >110mm2/m.
-
7/21/2019 s5 Ec8-Lisbon m Fardis
28/28
Check of tension chord between supports of the deep beam by walls W1.
Dissemination of information for training Lisbon 10-11 February 2011 28
Tension force in chord from moment equilibrium between:
,
uniform in-plane load of 1.728kN/m2 and force reactions to it at walls W1.
Internal lever arm in dee beam zL /2 and force in tension chord:(qELxLy
2/8)/(Lx/2) =qELy2/4.
Required steel area:As,t-chord=dqELy2/(4fyd)=1.1x1.728x25
2/(4x0.5/1.15)=2 2, . . . - .
Minimum design moment along chord is in the middle strip, giving surplusAs=(1-8.2/14.7)x10.2/(0.11x0.5/1.15)=94.4mm
2/m