seismic retrofitting of framed structures with stainless steel

8/13/2019 Seismic Retrofitting of Framed Structures With Stainless Steel

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Journal of Constructional Steel Research 62 (2006) 93104

www.elsevier.com/locate/jcsr

Seismic retrofitting of framed structures with stainless steel

L. Di Sarnoa,, A.S. Elnashaib, D.A. Nethercotc

aDepartment of Structural Analysis and Design, University of Naples, Federico II 80125, ItalybDepartment of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, IL 61820 USA

cDepartment of Civil and Environmental Engineering, Imperial College of London, SW7 2AZ UK

Received 18 November 2004; accepted 5 May 2005

Abstract

The appropriate use of special metals such as stainless steels (SSs) for structural applications in building systems provides possibilities

for a more efficient balance between whole-life costs and in-service performance. The present paper assesses the feasibility of the application

of SSs for seismic retrofitting of framed structures, either braced (CBFs) or moment resisting (MRFs) frames. In so doing, inelastic analyses

have been carried out on a set of multi-storey CBFs and MRFs. The results of both inelastic static (pushovers) and dynamic (response history)

analyses demonstrate that systems retrofitted with SSs exhibit enhanced plastic deformations and excellent energy absorbing capacity. The

augmented strain hardening of SS is beneficial in preventing local buckling in steel members in both MRFs and CBFs. The analytical

results also demonstrate that, when SS is spread within columns, the system over-strength increases by 30% with respect to the carbonsteel

benchmark structure. The design over-strength, plastic redistribution and energy dissipation capacity increase by the same amount.

2005 Elsevier Ltd. All rights reserved.

Keywords:Stainless Steel; Seismic design; Dissipation capacity; Inelastic analysis

1. Introduction

Earthquakes in California, Japan and Taiwan in the mid-

to-late 1990s severely damaged low-to-medium rise framed

steel and steelconcrete composite structures [1]. The struc-

tural damage was primarily caused by brittle fracture and

local buckling occurring in connections and/or brace mem-

bers [24]. As a result, several research projects were

launched worldwide to develop improved strategies for seis-

mic rehabilitation. Two retrofitting strategies emerged: the

local modification of material properties and/or seismic

details (e.g., beam-to-column connections) and the global

stiffening and strengthening of the lateral resisting sys-

tems.Fig. 1provides a comparison between the effects of

these local and global intervention schemes on the seis-

mic structural performance. The enhancement of stiffness,

strength, ductility and hysteretic dissipation in plan and over

the height of buildings should be carefully considered in

the seismic design and retrofitting of structures. The ob-

jective of local retrofitting is to increase the deformation

Corresponding author. Fax: +39 0 817 345036.E-mail address:[email protected] (L. Di Sarno).

0143-974X/$ - see front matter 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jcsr.2005.05.007

capacity of deficient components so that they will not reachtheir specified limit state as the building responds at the

design level (Fig. 1). Effective global upgrading strategies

should be able to increase the capacity of the structure

and/or decrease the demand imposed by the earthquake

loads. Structures with enhanced capacities may safely resist

the forces and the deformations induced by earthquake

response. Generally, global modifications to the structural

system are designed so that the design demands (target

displacement) on the existing structural and non-structural

components are less than their capacities. Lower demands

may reduce the risk of brittle failures in the structure and/or

avoid the interruption of its functionality.Novel materials, special metals, and/or technologies,

e.g. base isolation and supplemental damping, may be

employed for the seismic rehabilitation of framed buildings,

either braced (CBFs) or moment resisting (MRFs) frames.

Innovative metal materials that can be used for retrofitting

of steel structures are aluminium alloys, shape memory

alloys, and stainless steels. These metals possess unusual

characteristics that render them suitable in the field of

seismic rehabilitation [5]. These characteristics include
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94 L. Di Sarno et al. / Journal of Constructional Steel Research 62 (2006) 93104

Nomenclature

Abbreviations

CBF Concentrically braced frame

Cr Chromium

CS Carbon steelIF Irregular moment resisting frame

MRF Moment resisting frame

SS Stainless steel

UB Universal beam

UC Universal column

ULS Ultimate limit state

YLS Yield limit state

Symbols

dtop Roof lateral displacement

fy Yield strength

fu Ultimate strength

Htot Frame total heightq Behaviour factor

V Base shear

Vd Design base shear

Vu Base shear at ULS

Vy Base shear at YLS

W Frame seismic weight

D Horizontal displacement

y Yield elongation

u Ultimate elongation

y Proof stress

u Ultimate tensile strength

(i) mechanical properties, (ii) corrosion and heat resistance,

(iii) weldability, (iv) chemicalphysical compatibility with

other materials, (v) life cycle cost and (vi) recyclability.

The present work analyses the feasibility of the

application of SSs for seismic retrofitting of steel structural

systems for multi-storey buildings. In so doing, an outline

of the material properties relevant for seismic design is

provided. Design examples include moment resisting frames

(MRFs) and concentrically braced frames (CBFs) with

different amounts of SS spread within dissipative and/or

non-dissipative members. The seismic performance of the

sample frames is evaluated through inelastic static anddynamic analyses within the framework of performance

based assessment.

2. Stainless steel and seismic design

The commonest grades of SSs utilized for structural

applications include austenitic (ASS), ferritic (FSS), and

austeniticferritic (AFSS) or duplex. This classification is

based on the amount of chromium (Cr) present in the alloy

considered. Several applications already exist worldwide for

structural and non-structural components made of SSs, as

shown, for example, inFig. 2. Nonetheless, applications for

seismic design have not yet been investigated.

The stressstrain response of SS exhibits a smooth

transition between the elastic and inelastic branch.

Conventionally, a 0.20% offset permanent strain (proof

stress) is used to define the yield strength. A number of

experimental tests carried out primarily in Europe [6,7] andJapan [8] on austenitic (304 and 316) and austeniticferritic

grades of SSs have demonstrated that:

(i) The stressstrain curves of SS depart from linearity

at a much lower load level than for mild steel (CS).

Lower material yield is also typically found in SS.

Manufacturers can easily lower and/or increase proof

stresses due to tighter quality controls. These controls,

however, increase the cost of the material: SS is

approximately four times as expensive as CS.(ii) The ultimate elongation (u) and the ultimate-to-proof

tensile strength ratios (fu/fy) are on average higher than

for CS. For austenitic plates with thicknesses less than3 mm the values of u range between 35% and 40%

(S220), while a value of 4555% was found for greater

thicknesses; these values are, however, lower bounds.

Values of ultimate-to-proof tensile strength ratios can be

as high as 2.0 for SS.Fig. 3displays, for example, the

fu/fy ratios and deformations u for plates of various

thicknesses; these plates employ different grades of

316 austenitic grades. Minimum values of 50% are

common for u, whilst the fu/fy is not less than 1.50.

This is beneficial for seismic design due to enhanced

ductility. In fact, large inelastic deformations can be

accommodated if the material exhibits high values of

ultimate strain. In addition, the spread of inelasticityalong a member length, and hence its ductility, increases

with increase in fu/fystress ratios.(iii) Variations in both proof stress and tensile strength for

austenitic hot-formed plates are negligible, e.g. less than

45%. Coefficients of variation (COVs) for both proof

stresses and ultimate strengths for SS are smaller than

those for CS. The ultimate strength generally exhibits

less scatter than the proof stress. Negligible values

of COVs, e.g. less than 23%, ensure reliable control

of the failure mode, e.g. weak-beam, strong-column

response for moment resisting frames, whereby the

column is designed not for the applied action but foraction consistent with the over-strength of the beam.(iv) SS generally exhibits rather greater increases in

strengths at fast rates of loading [5,9]. The initial stress

state of the material has an effect on the strain rate. The

influence of the material strain rate sensitivity decreases

with increase in strain.(v) Austenitic SSs possess greater toughness than mild

steels [10,11]. The former are less susceptible to brittle

fracture than the latter for service temperatures down to

40 C. Fatigue tests with constant amplitude loading

have demonstrated that longitudinal and transverse non-

load carrying fillet welds for SS behave much better


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L. Di Sarno et al. / Journal of Constructional Steel Research 62 (2006) 93104 95

Fig. 1. Characteristics of global (top) and local (bottom) intervention approaches in seismic retrofitting.

Fig. 2. Structural (left) and non-structural (right) applications of stainless steel in modern buildings.

than equivalent welds in CS. Thus CS reference SN

curves underestimate the actual response of SS for the

same fatigue classes.

(vi) Experimental tests on SS beams, columns and beam-

to-column connections have shown large plastic

deformation capacity and energy redistribution at

section and member levels.

The above properties render SS an attractive metal

for applications in plastic and seismic design, particularly


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Fig. 3. Mechanical properties of stainless steel: material over-strength (left) and ultimate elongation (right).

Fig. 4. FEM models for sample MRFs (left) and CBFs (right).

for seismic retrofitting of steel, concrete and compositestructures. The suitability of the application of SSs for

seismic retrofitting is analysed herein with regard to multi-

storey framed structures, either MRFs or CBFs.

3. Applications: Design examples

To assess the feasibility of the application of SS to

the seismic retrofitting of steel building, a set of framed

structures, either moment resisting or braced, has been

selected and investigated in the inelastic range. Inelastic

static (pushover) and dynamic (response history) analyses

were carried out through refined models discretized through

FEM. The sample frames, the modelling assumptions and

the results of the investigations performed are provided

hereafter.

3.1. Moment resisting frames

A set of seven regular moment resisting frames (RFs) was

considered for the analytical study presented in this work.

The basic RF geometry consists of a three-baysix-storey

structure; the external and the internal bays are 8 m and 6 m

spans, respectively. The storey height is 3.5 m for all floors

with the exception of the ground floor, which is 4.5 m high.The concrete slab has a depth of 0.15 m and 0.12 m for floors

and roof, respectively. The grade for mild steel is S275;

similarly, a grade with proof stress of 275 MPa was used

for SS. Exterior columns employ UC 305, while interior

columns are in UC 356. Steel beams utilize UB 610 at all

but the top floor. Roof beams are UB 457. The characteristic

loads for floor finishes are 1 kN/m2 whilst, for imposed load,

5 kN/m2 and 3 kN/m2 at floor levels and roof, respectively,

have been considered. The frame in mild steel is assumed

as a benchmark for those systems in which SS has been

spread within beams and/or columns. The label RF(b10), for

instance, indicates that SS has been used for both ends of thebeams, for a length of 10% of the member span.

The IFs are derived from the RFs by bracing the external

bays in all but the first floor, in order to simulate the presence

of infills, thus creating a high concentration of inelastic

demand at the soft ground storey. A detailed description for

both RFs and IFs assessed in this study can be found in

Ref. [12].

3.2. Concentrically braced frames

Eight concentrically braced frames (CBFs) were de-

signed and assessed for this study. The geometric layout of


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Fig. 5. Spectral accelerations (left) and spectral velocity (right) for the earthquake ground motions used (damping = 5%).

Table 1

Characteristics of ground motions

Record Pr. of Exc. Magnitude Source distance PGA PGV PGD ARIAS intensity Duration (s)

(% in 50 yrs) (Mw ) (km) (g) (m/s) (cm) (m/s) Uniform Bracketed Significant

Morgan Hill 50 6.2 15 0.32 0.32 6.14 1.71 23.70 39.44 22.64

Whittier 50 7.3 17 0.77 0.92 11.32 5.42 10.38 37.10 8.70

Loma Prieta 10 7.0 12.4 0.66 0.70 18.41 4.24 13.00 35.22 11.30

Landers 10 7.3 36 0.42 0.36 16.08 2.10 22.98 47.90 22.28

Northridge 2 6.7 7.5 0.43 0.65 12.21 2.03 11.18 14.82 7.80

Kobe 2 6.9 3.4 1.28 1.46 30.31 14.61 9.38 16.46 6.86

the CBFs is similar to that of the MRFs. Braced frames em-

ploy six storeys and three bays. The storey height is set to

3.5 m for all floors with the exception of the ground floor,

which is 4.5 m high. CBFs utilize concrete slabs similar

to those used for the MRFs described in Section 3.1. Steel

grades and load values are similar to those given above for

MRFs. Exterior columns employ HEB 280, while interior

columns are in HEB 200. Steel beams utilize IPE 500 at all

but the floor. Roof beams are IPE 400. Three groups of diag-

onal braces were used; the dimensions of these braces vary

heightwise. Diagonals consist of circular hollow sections

with external diameters(d)varying between 115 mm (fifth

and sixth floors) and 210 mm (first and second floors); at the

third and fourth floors,d=165 mm. The average diameter-

to-thickness ratio is 30. The diagonals used to brace the cen-

tral bay of the multi-storey frame possess intermediate slen-

derness.In CBFs, SS was spread both in dissipative members

(braces) and non-dissipative components, such as beams and

columns. The system with all components in carbon steel is

assumed as a benchmark.

3.3. Structural modelling and analysis

The modelling of the sample frames described in

Sections 3.1 and 3.2 was carried out by means of the

finite element program ADAPTIC [13], a program for

static and dynamic large-displacement non-linear analysis

of space frames by adaptive mesh refinement. Bare frames

were modelled as two-dimensional assemblages of beam

members. Shear deformabilities of beams and columns were

also included in the structural model. Panel zone strengths

and deformations were not considered. Stiffnessand strength

due to concrete deck slabs were not accounted for in the

plane systems analysed; diaphragms are assumed rigid at

each floor. Five cubic elements were used to model both

beams and columns in MRFs, while braces in CBFs were

discretized through two cubic elements. Fig. 4 shows, as

example, the modellings adopted for typical MRFs and

CBFs. The refined analytical model ensures that spreads of

inelasticity and buckling, both local and global, are reliably

assessed. It is, in fact, ensured that three Gauss points lie

within each potential plastic hinge zone. Local buckling is

accounted for in ADAPTIC through the model formulated

by Elnashai and Elghazouli [14].The material modelling was based on the multi-

surface cyclic plasticity model given by Popov and

Petersson [15]. The uniaxial formulation based on the

modified RambergOsgood formula [16] was used in the

present study to model the skeleton curve of the material

response curve for SS. The relationships are as follows:

for y: =

E0+py

y

n(1)

for > y: =y

E0.2+pu

y

u y

n+ty (2)


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Fig. 6. Capacity curves for the sample regular (top) and irregular (bottom) MRFs.

Fig. 7. Capacity curves for the sample CBFs: spreading of SS in single members (left) and hybrid members (right).

where n and n are parameters to be calibrated by fitting

the experimental curves, py and pu are the plastic strains

corresponding to the 0.2% proof stress (y) and ultimate

strength (u), respectively, while ty is the total strain

corresponding to y. E0 and E0.2 are the initial and the

proof stress moduli. Further details of the values assumed

for the model parameters can be found in Ref. [12].

For the mild steel, the ratio of the strain hardening

(Esh) to the initial stiffness (E0) was assumed equal to

Esh/E0 = 3%. The section yield capacity was evaluated

in the present work by taking into account momentthrust

interaction for both the beams and the beamcolumn

elements.

Comparative analyses of the seismic structural perfor-

mances of carbon, SS and hybrid MRFs, either regular

(RFs) or irregular (IFs), were carried out on a set of 14

frames. Inelastic static (pushovers) and dynamic (response

history) analyses were performed by means of ADAP-

TIC [13]. For CBFs, the total number of assessed frames

is 22.


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Pushover (static) analyses were performed through

displacement-controlled patterns, both inverted triangular

and rectangular. Response history analyses were conducted

by using a set of ground motions corresponding to different

seismic hazards as detailed in the next section.

3.4. Earthquake ground motions

Dynamic response histories were carried out employing

suites of ground motions developed for the FEMA-SAC

steel project in the USA [17]. These earthquakes include

horizontal records matching the 1997 NERHP design

spectrum [18]. The seismological properties of the records

used for this study are summarized inTable 1. Three levels

of seismic hazard were employed: 50%, 10% and 2%

probability of exceedence in a 50-year period.

The distances from the sources for the records used to

carry the inelastic analyses range between 3.4 km (Kobe,

in Japan) and 36 km (Landers, in California). Therefore,

the above suite of strong motions covers a range ofdesign scenarios (near- and far-field). In this study near-

and far-field records were chosen to compare seismic

performance during earthquakes with different frequency

contents (Fig. 5).

The values of the duration and energy content, expressed

as ARIAS intensity, of the records summarized in Table 1

show that Kobe is the shortest record but the most

demanding in terms of input energy.

3.5. Seismic performance criteria

Performance levels can be specified as limits on anystructural response parameter, e.g. actions (stresses, forces,

moments) and deformations (strains, displacements and

rotations). Obviously, different limit states have to be cross-

correlated to the level of the earthquake design level (seismic

input). In this study four structural performance levels

have been checked in compliance with guidelines given by

SEAOC [19] and FEMA [20]. The relationship between

overall seismic performance and maximum transient drift

ratios is summarized inTable 2.

Table 2

Structural performance levels (afterSEAOC, 1999)

Performance Qualitative Damage Recommended

level description type storey drifts (%)

SP-1 Operational Negligible 0.5

SP-2 Occupiable Light 1.5

SP-3 Life safety Moderate 2.5

SP-4 Near collapse Severe 3.8

The three main dynamic response parameters, stiffness,

strength and ductility assume a paramount role in the

behaviour of structures. In order to comply with the SP-1

performance target the structure needs enough stiffness to

ensure that non-structural damage is minimized. Sufficient

Fig. 8. Global overstrength and plastic redistribution for the sample regular

(top), irregular (middle) and concentrically braced (bottom) frames.

strength to ensure elastic behaviour and avoid structuraldamage under small/medium events is also required to

guarantee fulfilment of the SP-2 target. Finally, in the

case of a severe earthquake, ductility plays a key role

in the maintenance of its strength and ensures the

fulfilment of SP-3 and SP-4 prerequisites. The deformational

quantities monitored herein are global response parameters,

i.e. the inter-storey (d/ h) and roof (dtop/Htot) drifts.

Structural over-strengths (Vy/Vd and Vu/ Vy) and force

reduction factors (Vu/ Vd) were also computed by means

of inelastic static analyses. Additionally, base storey shears

are investigated to assess the effects of the SS on the

force demand in the sample structures. The values of the


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Fig. 9. Roof drifts of regular (left) and irregular (right) MRFs subjected to Morgan Hill (top), Landers (middle) and Kobe (bottom) earthquakes.

design base shear were computed in compliance with Vdfrom European seismic standards [21]. The values of the

above deformation and resistance response parameters are

discussed hereafter.

3.6. Inelastic performance assessment

The structural seismic performance of the sample MRFs

and CBFs was assessed in terms of global response param-

eters, either resistance (base shears and over-strengths) or

deformation capacity (interstorey and roof drifts).

3.6.1. Resistance

The lateral resistance capacity of the sample frames is in-

vestigated through the pushover analyses.Figs. 6and7pro-

vide the pushover curves obtained for MRFs by considering

displacement controlled horizontal patterns (triangular dis-

tribution) for regular and irregular frames, respectively.

It is shown that the enhancement of structural perfor-

mance can be significant for the frames with columns in

SS. For example, the system over-strengths of RF(c20) and

RF(c100) are 2530% higher than for the benchmark frames

in mild steel. However, spreading SS in columns is not found

to be more efficient and cost-effective than using SS only

at the column ends. The increased over-strength character-

izes both regular (RFs) and irregular (IFs) configurations.

For IFs, spreading of SS in columns has also been found

beneficial for the prevention of local buckling. The high

strain hardening of the material delays the onset of insta-

bility, which usually occurs in the inelastic range.

Fig. 8 shows the results of the static pushover analyses

for CBFs. SS has been used for dissipative (braces) and


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Fig. 10. Roof drifts of CBFs subjected to Morgan Hill ( top), Landers (middle) and Kobe (bottom) earthquakes.

non-dissipative (beams and columns) members. Hybrid

configurations, e.g. with braces and beams, braces and

columns and beams and columns, have also been considered.

It is found that the systems exhibit higher over-strength when

SS braces and/or SS columns are employed. In particular, byusing SS braces and columns the increase in over-strength is

about 33% with respect to the configuration in mild steel.

Fig. 8 summarizes the values of global over-strengths

(Vy/ Vd and Vu/ Vy) for the sample frames, both MRFs and

CBFs. The values are compared to those of benchmark

frames in carbon steel. It may be observed that the round-

house behaviour of SS and its high material over-strength

(fu/fy) causes global lateral resistance to continue to

increase, even at large drifts. The enhancement is about

2530% for RFs with 20% of SS at both ends of columns.

For CBFs, the maximum values of Vy/ Vd and Vu/ Vy, i.e.

about 30%, can be reached for frames with SS in both braces

and columns.

The effect of SS in the seismic base shear of the sample

frames was computed through inelastic both static and

dynamic analyses. Figs. 11 and 12 provide the variations

of the seismic coefficient, i.e. dimensionless base shear

Vb/ Wtot, with Vb the base shear and Wtot the total seismic

weight of the structure, during the Morgan Hill, Landers and

Kobe ground motions. These earthquakes exhibit different

probabilities of exceedence, i.e. 2% (Kobe), 10% (Landers)

and 50% (Morgan Hill).

The results show that the use of SS in structural members

(beams, columns and braces) mitigates the maximum

seismic base shear demand. This effect is significant for

ground motions with both low (Morgan Hill) and high

(Kobe) probabilities of exceedence. For ground motions


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Fig. 11. Dimensionless base shears of regular (left) and irregular (right) MRFs subjected to Morgan Hill (top), Landers (middle) and Kobe (bottom) earthquakes.

with 10% probability of exceedence, the benefits in using

SS in structural members is minimal; the response is

however dependent on the seismological characteristics ofthe earthquake records used in the analysis. The above

results were found for both MRFs and CBFs. The use of

SS in columns (MRFs) and bracecolumns (CBFs) leads to

significant reductions (2530%) of the shear seismic demand

on the framed structures. The reduction of the shear is higher

in the IRs than in RFs.

3.6.2. Deformations

The deformation capacity of the sample frames was

investigated through the pushover curves provided inFigs. 6

and 7. The ultimate deformation capacity of MRFs and

CBFs is significantly enhanced by the use of SS braces and

columns: values of lateral drifts (dtop/Htop) are 1015%

higher than those for frames in mild steel. CBFs with SS ineither braces or columns exhibit the same seismic response.

There are no benefits in using SS in the beams of CBFs. The

enhanced seismic performance of CBFs can be attributed to

the prevention of local buckling which often undermines the

energy dissipation capacity under earthquake loads.Table 3

summarizes the values of ductility estimated at different

performance levels for CBFs. It can be noted that the values

of ductility can be, at the Near Collapse limit state, as

high as 10.30 for the frame SS(bmcol) and 10.45 for the

case SS(brcol). These values are close to those relative to

the benchmark structure SS(all), i.e. 10.47. At Occupiable


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Fig. 12. Dimensionless base shears of CBFs subjected to Morgan Hill ( top), Landers (middle) and Kobe (bottom) earthquakes.

and Life Safe the variations of the values of ductility are

less significant than in the case of Near Collapse. Similar

results were found also for MRFs, either regular (RFs) or

irregular (IFs).

The use of SS in braces and/or columns of CBFs may be

effective in reducing the lateral deformability and enhancing

the damping characteristics of the structural system.Figs. 9

and 10, for example, show the time history of roof drifts

for CBFs subjected to earthquake ground motions with

probabilities of exceedence of 50% (Morgan Hill), 10%

(Landers) and 2% (Kobe). The values of the drifts are plotted

as a percentage of the frame total height.

For both Morgan Hill and Landers earthquakes, all the

configurations are compliant with the operational limit

state as shown in Figs. 9 and 10. It is also observed that

Table 3

Ductility at different performance levels for CBFs

Frame Operational Occupiable Life safety Near collapse

CS(all) 1.00 3.30 6.30 7.32

SS(bm) 1.00 3.28 6.27 7.30

SS(all) 1.00 4.07 6.70 10.47

SS(br) 1.00 4.02 6.73 10.40

SS(col) 1.00 5.07 6.00 9.43

SS(brcol) 1.00 4.05 6.72 10.45

SS(brbm) 1.00 3.90 6.67 9.37

Ss(bmcol) 1.00 3.87 6.03 10.30

the use of SS braces leads to damping in top drifts as high

as 50%. For the Kobe earthquake, the braced structures


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exceed the threshold of 0.50%; for Kobe the maximum

top drift is about 0.90%. The values of the maximum

roof drifts (dtop/Htop) do not exceed the value of 1.50%

(Occupiable) for the Kobe earthquake. Conversely, when

the Northridge record was used, the maximumdtop/Htop is

nearly 4.0%, thus giving rise to severe structural damage;

the threshold of the performance level Near Collapse isovercome.

Under the Landers record the use of SS in braces

and/or columns does not give rise to any beneficial effect.

The maximum drifts are increased by spreading SS in

members. This dynamic response may be attributed to the

seismological characteristics of the ground motions utilized.

Further analytical investigations are under way to shed

light on the effects of near-fault effects on the seismic

response of CBFs with SS in dissipative and non-dissipative

members.

4. Conclusions

Extensive inelastic static (pushovers) and dynamic

(response history) analyses were carried out in the present

study for both MRFs and CBFs. The results demonstrate that

SSs possess enhanced plastic deformations and excellent

energy absorbing capacity. The augmented strain hardening,

which is nearly twice that of carbon steels (2.30 versus

1.20), may reduce the likelihood of local buckling in steel

members in both MRFs and CBFs. The analyses carried

out demonstrate that for MRFs when SS is spread within

columns, the system over-strength increases by 30% with

respect to the carbonsteel benchmark structure. The design

over-strength, plastic redistribution and energy dissipationcapacity increase by the same amount. The study also

reveals that there is no significant benefit in spreading SS

within beams (dissipative members). The onset of yielding

in dissipative members is delayed when SS is employed.

On the other hand, in CBFs with SS braces and columns

the increase in over-strength is about 33% with respect

to the configuration in mild steel. Values of lateral drifts

(dtop/Htop)for CBFs with SS are 1015% higher than those

for frames in mild steel. There are no benefits in using SS in

beams of CBFs.

Acknowledgements

This work was supported in part by the Earthquake

Engineering Research Centers Program of the National

Science Foundation under NSF Award Number EEC

97-01785. Any opinions, findings and conclusions or

recommendations expressed in this material are those of the

authors and do not necessarily reflect those of the National

Science Foundation.

References

[1] Federal Emergency Management Agency. State of Art Report on past

performance of steel moment frame buildings in earthquakes. Report

No. FEMA 355E, Washington, DC, USA; 2000.

[2] Bruneau M, Uang CM, Whittaker AS. Ductile design of steel

structures. New York (USA): McGraw Hill; 1998.

[3] Mahin SA. Lessons from damage to steel buildings during the

Northridge earthquake. Engineering Structures 1998;20(4):26170.

[4] Watanabe E, Sugiura K, Nagata K, Kitane Y. Performances

and damages to steel structures during 1996 HyogokenNanbu

earthquake. Engineering Structures 1998;20(46):28290.

[5] Di Sarno L, Elnashai AS. Special metals for seismic retrofitting

of steel and composite buildings. Journal of Progress in Structural

Engineering and Materials 2003;5(2):6076.

[6] Burgan BA, Baddoo NR, Gilsenan KA. Structural design of stainless

steel members: Comparison between Eurocode 3, Part 1.4 and tests

results. Journal of Constructional Steel Research 2000;54(1):5173.

[7] Johansson B, Olsson A. Current design practice and research on

stainless steel structures in Sweden. Journal of Constructional Steel

Research 2000;54(1):329.

[8] Aoki H. Establishment of design standards and current practice for

stainless steel structural design in Japan. Journal of ConstructionalSteel Research 2000;54(1):191210.

[9] Euro Inox. Design manual for structural stainless steel. 2nd ed.

Toronto: NiDi; 2002.

[10] Eurocode 3. Design of steel structures. Part 1.4General rules

Supplementary rules for stainless steel. Brussels: European Commis-

sion for Standardization; 1996.

[11] Gardner L. The use of stainless steel in structures. Journal of Progress

in Structural Engineering and Materials 2005;7(2):4555.

[12] Di Sarno L, Elnashai AS, Nethercot DA. Seismic performance

assessment of stainless steel frames. Journal of Constructional Steel

Research 2003;59(10):1289319.

[13] Izzuddin BA, Elnashai AS. ADAPTIC, a program for the adaptive

large displacement elasto-plastic dynamic analysis of steel, concrete

and composite frames. ESEE research report No. 7-89, London (UK);

Imperial College, 1989.[14] Elnashai AS, Elghazouli AY. Performance of composite

steel/concrete members under earthquake loading. Part I: Ana-

lytical model. Earthquake Engineering and Structural Dynamics

1993;22(4):31545.

[15] Popov EP, Petersson H. Cyclic metal plasticity: Experiments and

theory. Journal of the Engineering Mechanics Division 1978;

104(EM6):137188 [Proceedings of the American Society of Civil

Engineers].

[16] Mirambell E, Real E. On the calculation of deflections in structural

stainless beams: An experimental and numerical investigation. Journal

of Constructional Steel Research 2000;54(1):10933.

[17] Somerville P, Smith N, Punyamurthula S, Sun J. Development of

ground motion time histories for Phase-2 of the FEMA/SAC Steel

Project. Report No. SAC/BD-97-04, Sacramento, CA, USA; 1997.

[18] Federal Emergency Management Agency. NERPH recommendedprovisions for seismic regulations for new buildings. FEMA Report

No. 302, Washington, DC; 1997.

[19] Seismology Committee Structural Engineers Association of Califor-

nia. Recommended lateral force requirements and commentary. 7th

ed. California; 1999.

[20] Federal Emergency Management Agency. Pre-standard and commen-

tary for the seismic rehabilitation of buildings. Report No. FEMA 356,

Washington, DC, USA; 2000.

[21] Eurocode 8. Design of structures for earthquake resistance. Brussels:

European Commission for Standardization; 1998.

seismic retrofitting of framed structures with stainless steel

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