1. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona DiSGG, Università della Basilicata, Potenza DiSGG, Università della Basilicata, Potenza 27° Convegno Nazionale GNGTS Trieste 6-8 ottobre 2008 Angelo MASI, Marco VONA VALUTAZIONE NUMERICA E SPERIMENTALE DEL PERIODO DI VIBRAZIONE DI EDIFICI ESISTENTI IN C.A.

2. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona STATEMENT OF THE PROBLEM The effects of seismic actions on buildings can be determined using various methods of analysis. Assuming a linear-elastic behaviour of the structure, two methods can be used: - the lateral force method of analysis (LFMA), for simple buildings; - the modal response spectrum analysis (MRSA), applicable to all types of buildings. Both methods make use of an elastic ground acceleration response spectrum (elastic response spectrum) in the evaluation of the seismic response, where the calculation of the fundamental period T1 (LFMA) or periods (MRSA) of the structure has a main role.

3. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona STATEMENT OF THE PROBLEM For the determination of T1, expressions based on methods of structural dynamics (e.g. Rayleigh method) may be used: Alternatively, many design codes provide simple expressions to calculate T1 that depend on: - building material (concrete, steel, masonry, etc.), - building type (frame, shear wall, etc.), - and overall dimensions (height, plan length, etc.).

4. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona Simplified Period – Height Relationship The typical form of the simplified relationship is as follows: T 1 = C t H α where C t and α are coefficients theoretically or experimentally derived.

5. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona Simplified Period – Height Relationship Force Based Design

6. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona OBJECTIVE OF THE STUDY Main objective of the study is the derivation of period-height expressions for classes of European RC buildings. Relationships from design codes and reported in the literature have been examined and their results have been compared to those ones obtained from numerical simulations (eigenvalue analyses) and ambient vibration analyses. Numerical simulations A wide parametric analysis on structural types representative of typical RC buildings have been carried out. Ambient vibration analyses Based on measurements carried out using quick survey techniques and/or permanent installations.

7. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona NUMERICAL SIMULATIONS Parametric Analysis Parameters of numerical simulations Number of Story: 3 cases Dimensions in Plan: 2 cases Irregularity in Elevation: 3 cases Presence and position of Masonry Infills: 4 cases Member Stiffness: 3 + 3 cases Variation in member stiffness is due to beam dimensions (Rigid Beams or Flexible Beams) and to effect of cracking A parametric analysis has been carried out on several structural types purposely selected and designed representative of typical European RC buildings designed only to vertical loads

8. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona STRUCTURAL CODES IN FORCE HANDBOOKS TYPICALLY USED DESIGN CURRENT PRACTICE SIMULATED DESIGN (only gravity loads) Internal forces computation: simplified models Reinforcement design (amount, details) Information Source (from the period of construction ) STRUCTURAL TYPES SELECTION and DESIGN TYPICAL RC STRUCTURES INVENTORY STRUCTURAL TYPE SELECTION Simulated Design of Existing R/C Buildings

9. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona 4 Story 2 Story 8 Story PARAMETRIC ANALYSIS: NUMBER of STORY

10. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona Totally Infilled Frames (IF, Infilled Frame) Partially Infilled Frames (PF, Pilotis Frame) Without Infill Frames (BF, Bare Frame) PARAMETRIC ANALYSIS: POSITION of INFILLS and BEAM STIFFNESS 2 story 4 story 8 story Beam Stiffness

11. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona 2 story4 story PARAMETRIC ANALYSIS: IRREGULARITY in ELEVATION 8 story Totally Infilled Frames (IF, Infilled Frame) Partially Infilled Frames (PF, Pilotis Frame) Without Infill Frames (BF, Bare Frame)

12. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona PARAMETRIC ANALYSIS: EFFECT OF CRACKING ON MEMBER STIFFNESS Eurocode 8: Design of structures for earthquake resistance - Part 1: General rules, seismic actions and rules for buildings In concrete buildings the stiffness of the load bearing elements should, in general, be evaluated taking into account the effect of cracking. Unless a more accurate analysis of the cracked elements is performed, the elastic stiffness properties of concrete elements may be taken to be equal to one-half of the corresponding stiffness of the uncracked elements I e / I gross = 0,5 Experimental results (e.g. Kunnath et al., 1995) show that different values I e / I gross can be adopted to take into account the different effect of cracking on columns and beams (role of the axial load value). Kunnath, K.S., Hoffmann, G., Reinhorn, A.M., Mander, J.B.,, Gravity load designed reinforced concrete buildings - part I: seismic evaluation of existing construction, ACI Structural Journal, May – June, 1995

13. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona RESULTS OF NUMERICAL SIMULATIONS Effects of Cracking and role of Infills (BF and IF types) I gross I e = 0.7 I gross I gross I e = 0.7 I gross Lower values Lower scatter Higher values Higher scatter

14. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona RESULTS OF NUMERICAL SIMULATIONS MAX MIN PF IF LF1

15. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona PROPOSED PERIOD-HEIGHT RELATIONSHIP

16. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona EXPERIMENTAL RESULTS Italian RC Building Stock (Gallipoli et al., 2006) Microtremor measurements on 50 RC Italian buildings have been performed in Potenza town (Southern Italy) and in Senigallia town (Central Italy) RC buildings under examination were designed taking into account only gravity loads, and were constructed in the period 50s - 70s The buildings exhibit strongly different characteristics both in plan and in elevation Simple and reliable methodologies have been used to estimate the fundamental period of buildings Using a three component data acquisition system, the horizontal and vertical components of microtremors at the base and the top of the buildings are recorded

17. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona EXPERIMENTAL RESULTS Some examples of Italian RC Buildings Pilotis Building Irregular in Elevation Building

18. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona REGRESSION of EXPERIMENTAL RESULTS + SD - SD

19. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona EXPERIMENTAL RESULTS Spanish RC Buildings (Navarro et al., 2004) The dynamic behaviour characteristics of 89 RC building structures were investigated using microtremor measurements. The measurements were performed at the top of the buildings and at the centre of plan on the roof floor or at the last story of buildings. The dominant type of construction in Granada City consists in RC frames without earthquake-resistant design, with unidirectional RC tile lintel floors and exterior hollow brick walls. The RC buildings under examination were regular both in plan and elevation. Proposed period-height relationship: T1 = 0,016 H

20. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona NUMERICAL VS. EXPERIMENTAL RESULTS

21. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona Most damaged building A striking damage pattern appeared in the town of Bonefro. A VII MCS intensity was estimated for the whole town, with light damage in the historical centre. Two RC buildings, located on soft sediments, close to each other (10 m) and very similar in design and construction, with the exception of their height (4 stories vs. 3 stories), suffered very different damage: D4-EMS in the 4 stories bldg, D2 in the other one. To investigate a possible cause of the damage difference, during the survey it was decided to evaluate the frequency of the two bldgs, by recording ambient noise. The measurement was under way just when the 1 Nov. M=5.3 shock took place, thus making possible to get the first strong-motion measurement inside an European building while it was suffering heavy damage by an earthquake. EXPERIMENTAL RESULTS BONEFRO Building (MOLISE 2002 Earthquake)

22. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona After October, 31 (ML 5.4)After November, 1 (ML 5.3) EXPERIMENTAL RESULTS BONEFRO Buildings

23. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona November, 1 Earthquake EXPERIMENTAL RESULTS BONEFRO Buildings

24. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona EXPERIMENTAL RESULTS CInEnel Building

25. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona DYNAMIC CHARACTERISTIC IDENTIFICATION EXPERIMENTAL RESULTS CInEnel Building

26. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona DYNAMIC CHARACTERISTIC IDENTIFICATION EXPERIMENTAL RESULTS CInEnel Building Building 1 (Structural Damage) Building 2 (No Damage) Building 1 Building 2 Mode 1Mode 2Mode 1Mode 2 Experimental 0.2560.2420.2280.217 ATC, EC80.572 NZSEE0.686 NEHRP, Goel-19970.533 Hong-20000.259 Chopra-2000, DBD0.767 Crowley-2004, DBD1.500

27. 27° GNGTS, Trieste, 6-8 ottobre 2008 A. Masi, M. Vona FINAL REMARKS Fundamental period has a main role in the determination of the effects of seismic actions on buildings The strong influence of masonry infills and of cracking on the fundamental period values of RC buildings has been highlighted Simplified period-height expressions are provided purposely set up for some structural types widely present in the European built environment Further studies and in-situ tests are needed to better understand the large differences between numerical and experimental values Experimental results on damaged RC buildings show low period increase (frequency decrease) as a consequence of heavy damage levels