İhsan engin bal · 2017. 7. 4. · İhsan engin bal research group on earthquake resistant...

Introduction &Recent Research in Groningen Earthquakes

İhsan Engin BAL

Research Group on Earthquake Resistant Structure

Displacement-Based Earthquake Loss Assessment: Method Development and Application to Turkish Building StockI.E. Bal, H. Crowley, R. PinhoResearch Report Rose 2010/02

Motivation for earthquake engineering…

THE RESPONSE OF UNREINFORCED MASONRY

TO LOW-AMPLITUDE RECURCIVE LOADS:

CASE OF GRONINGEN GAS FIELD

COMPDYN 2017

İhsan E. Bal, Eleni Smyrou and Dimitrios Dais

Introduction to Induced Seismicity

• The largest gas field in Europe

and 10th in the world

• No earthquakes were reported

from the Groningen area prior to

1991

• Before smaller than the humanly

perceptible levels

In 2014 Oklahoma actually surpassed the San Francisco region, famous for its seismic excitations, in terms of the rate of earthquakes

Oklahoma region is lacking of any important fault

Introduction to Induced Seismicity – Case of Oklahoma

low magnitude normally cannot be perceived by humans

Induced seismicity events are felt due to their shallow depth

(e.g. for Groningen the depth is 3 km)

Induced vs Deep Natural Earthquakes

• The gas field was discovered in 1959

• Gas Initially In Place (GIIP): 3000 billion m3 (bcm)

• Until 2015, 75% of the GIIP had been extracted

• Annual number of earthquakes has been

increasing since 2003

• Correlation between gas production - seismicity

Groningen Gas Field

Low magnitude Excitation

vs

Moderate Scale Damages

Motivation of the Study– Groningen Paradox

Damages in the Region

• 60,000 homes lie within the earthquake

zone

• 40,000 properties are considered at risk of

damage and are under inspection

• 6,000 damage claims

• Value of properties has decreased

drastically

• Rising uncertainty

• 1-story or 2-story houses compose the main building stock, mostly URM

• Lack of seismic design – no seismic loading was expected

• Low normal stresses (low shear strength) on the load bearing and veneer walls

• Limited experimental research on the low-cycle fatigue of masonry under recursive loads

• Further investigation of URM response in low-amplitude range is required

• Shallow quakes (3km depth) release more energy at the surface - limited area that is

affected, but higher intensity is attained

Particularities of the Groningen Problem

• Low-rise and stiff structures with low natural period

• Resonance between the excitation and the structures (?)

• Poor soil conditions (soft clay with 40kPa allowable strength !)

• Unlikely with most of the similar cases, Groningen gas field is densely populated

Motivation of the Study– Groningen Paradox

Maximum intensity : VI

magnitude Mw : 3.6

Recorded PGA : 85 cm/s2

From Codes : 10 cm/s2

Recorded PGV : 3.45 cm/s

Focal Depth: 3 km (quite shallow)(EMS98 intensity grades)

2012 Huizinge (Groningen) EQ, Mw=3.6

The August 16th, 2012, Earthquake Near Huizinge (Groningen)

PGA 85 cm/s2

T : 0 - 0.5 sec

Wavelet Analysis (Tectonic Event on Soft Soil)

Smyrou E., Bal İ. E., Tasiopoulou P., and Gazetas G., “Wavelet analysis for relating soil amplification and liquefaction effects with seismic performance of precast structures, ”, Earthquake Engineering and Structural Dynamics, (2016)

Wavelet analysis from a tectonic earthquake recorded on soft soil

Frequency Issue

Wavelet Analysis (Induced Seismicity)

2012 EQ, Groningen 2014 EQ, Groningen

Wavelet Analysis (Tectonic Events)

2012 EQs, Emilia-Romagna, Italy

The August 16th, 2012, Earthquake Near Huizinge (Groningen)

Before the Event

According to studies, induced seismic events with M < 3.9

NO significant structural damage

Low Risk

The August 16th, 2012, Earthquake Near Huizinge (Groningen)

After the Event

safety of the citizens might be at risk

Updated seismic hazard analyses : Mmax = 5

Quite a Catastrophic Scenario

Available Experiments on Groningen-type URM

Sponsored by NAM

Conducted by EUCENTRE

(Pavia, Italy)

In-Plane Cyclic Shear-

Compression Tests

Slender Squat

Available Experiments on Groningen-type URM

Fy = 60 kN, δy = 0.45 mm, δu = 8.2 mm

Response of Squat Wall

Available Experiments on Groningen-type URM

max SA (Huizinge, 2012) = 2.2 m/sec2

mass = 13 tn

Squat Wall

Fb = m * SA = 28.6 kN << Fy = 60 kN

ZERO damage

would be expected

BUT…

Available Experiments on Groningen-type URM

Full-scale Building Test First Cracks

test #16 : PGA = 1.6 m/s2

PGA (Huizinge, 2012) = 0.85 m/sec2 << test #16 : PGA = 1.6 m/s2

Available Experiments on Groningen-type URM

Response of Squat Wall

1st cycle

Stress Drop in Small Cycles

Cyclic response in large cycles

Force

Displacement

Force

Displacement

Cyclic response in small cycles

Available Experiments on Groningen-type URM

first 3x3 cyclesidealized hysteresis

backbone (still working on it !)

1) Δfi

2) αΚi

3) dres

Exercise with Existing Hysteresis Loops – Cyclic Loading

Ramberg–Osgood Model in

SeismoStruct Software

Exercise with Existing Hysteresis Loops – Cyclic Loading

Next Steps

I. E. Bal et al., 2010

Exercise with Existing Hysteresis Loops – Seismic Loading

Exercise with Existing Hysteresis Loops – Seismic Loading

• Full database for 2014

• Proximity to Huizinge epicenter

• Distribution of earthquakes

(1 M3 & 18 1.5≤M<3)

Exercise with Existing Hysteresis Loops – Seismic Loading

Seismic Scenarios

1) Huizinge (2012)

2) 1-year + Huizinge (2012)

3) 5-year + Huizinge (2012)

4) 10-year + Huizinge (2012)

Exercise with Existing Hysteresis Loops – Seismic Loading

Analysis

δmax : 0.06 mm

Test

δy = 0.45 mm & δu = 8.2 mm

NOT destructive acting on its own

Exercise with Existing Hysteresis Loops – Seismic Loading

Conclusions

Conclusions

• Experimental evidence show that the response of the Groningen-type URM walls is quite

different in the very first cycles then in the post-yield phase

• The available hysteresis loops are designed to capture more accurately the post-yield phase,

and thus are not suitable for the small amplitude cycles

• The most well calibrated model was not able to present any cumulative damage, and even

has tendency to re-center, contradicting the expectations and previous experimental

findings under normal stress cases

Exercise with Existing Hysteresis Loops – Seismic Loading

• There is a characteristic force drop in the small amplitude cycles in case of unloading, which

cannot be modeled by using the widely available common hysteresis loops

• A special hysteresis rule that represents not only the large displacement and the post-yield

phase but also the very small amplitudes need to be developed.

Thank you