- Rehabilitation of earthquake damaged external RC beam-column joints
- J. Shafaei ; A. Hosseini ; M.S. Marefat ; J.M. Ingham
- Book Title / Journal: New Zealand Society for Earthquake Engineering (NZSEE) Annual Technical Conference
- Year: 2014 , Volume: , Series:
- Repair and Retrofit of Structures
- Keywords: RC buildings ; Earthquake ; beam-column joints ; Seismic performance
- Description
- Post-earthquake inspections of damaged RC buildings have demonstrated that poorly detailed beam-column joints can suffer serious damage. The effectiveness of a rehabilitation method based on joint enlargement using prestressed steel angles to
enhance the seismic behaviour of damaged external reinforced concrete beam-column joints was experimentally investigated. Three half scale external RC beam-column joints with seismic and non-seismic reinforcement details were tested before and after rehabilitation by applying lateral cyclic loading of increasing amplitudes. Tested
specimens were comprised of one unit having seismic reinforcement detailing and two units having non-seismic reinforcement detailing. Two defects were considered for the non-seismic units, being the absence of transverse steel hoops and insufficient bond capacity of beam bottom steel reinforcing bars in the joint panel zone. The damaged specimens were rehabilitated by injecting epoxy grout into existing cracks and installing stiffened steel angles at the re-entrant corners of the beam-column joint, both above and below the beam, that were mounted and held in place using prestressed high tensile strength bars. The test results indicated that the seismic performance of the rehabilitated
specimens, in terms of strength, stiffness and ductility were fully recovered with respect to the performance of the seismically detailed specimen in the initial loading.
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- FRG strengthening systems for masonry building
- A. Balsamo ; I. Iovinella ; G. Morandini
- Book Title / Journal: New Zealand Society for Earthquake Engineering (NZSEE) Annual Technical Conference
- Year: 2014 , Volume: , Series:
- Repair and Retrofit of Structures
- Keywords: masonry buildings ; Fiber-Reinforced Grouting ; Fiber-Reinforced Polymer
- Description
- Up to the middle of the last century the main building material was masonry, that is why in most countries there are many masonry buildings and many of these have great historical or social value.
These buildings, located in seismic areas, due to their age are deteriorated by environmental and human factors. This combination of factors causes a very alarming situation that causes a growing interest toward a new strengthening system. Researchers are orientated toward a less invasive and reversible system possibly avoiding resin and
organic materials.
Thanks to recent applications, especially on historical buildings, it was possible to realize a strengthening system based on application of FRP grid and mortar matrix (FRG). Much experimentation was conducted to test the effectiveness of this technology on different kinds of masonry.
The present paper resumes the latest tests carried out by the University of Naples on different masonry panels tested under diagonal compression.
Experimental campaign investigated preliminarily on material properties of based component from bricks to reinforcing mortar. The experimental results confirmed the effectiveness of the investigated strengthening technique to increase the panels shear strength and validated the effectiveness of this reinforcing sysTem on different kinds of masonry.
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- Advances in design requirements for Buckling Restrained Braced frames
- K.S. Robinson
- Book Title / Journal: New Zealand Society for Earthquake Engineering (NZSEE) Annual Technical Conference
- Year: 2014 , Volume: , Series:
- Structure types ; Steel structures
- Keywords: Buckling Restrained Braced frames ; design requirements
- Description
- Although buckling restrained braces (BRB) have now been a codified system in the US for over five years and have been used in design for much longer, the
system is still relatively new in New Zealand. BRB’s are now entering their second US code cycle with the AISC Seismic Provisions for Structural Steel Buildings, AISC 341-10, which has introduced significant changes. In addition, several key issues of current research will be discussed that are contributing to the next set of code requirements for 2016. These new changes will be highlighted along with methods to effectively design Buckling Restrained Braced Frames (BRBF) using New Zealand codes. The latest innovative uses for BRBs will also be discussed, including applications to alleviate
building pounding concerns when seismic joints are of limited size, many different configurations possible for retrofit construction, ideas for high rise applications, and other unique applications.
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- Review of buckling restrained brace design and behaviour
- A.S. Jones ; C-L Lee ; G.A. MacRae ; G.C. Clifton
- Book Title / Journal: New Zealand Society for Earthquake Engineering (NZSEE) Annual Technical Conference
- Year: 2014 , Volume: , Series:
- Structure types ; Steel structures
- Keywords: Buckling restrained braces ; brace design
- Description
- Buckling restrained braces (BRBs) have become a popular alternative to traditional bracing in seismic loading due to their ability to develop full and balanced hysteresis loops resulting in similar tension and compression capacities. However, research internationally for the design and behaviour of BRB compositional elements is still in the infancy stage, with intellectual property rights by commercial providers within America and Asia limiting the available research.
This paper considers the history and development of BRBs (steel-concrete and steel-steel), current design practice, areas for further development and forthcoming research to be carried out that the University of Canterbury. The outcomes of this research which consider the sensitivity in BRB member design aims to equip engineers with an understanding of BRBs but also the ability to design BRBs without the need for testing verification.
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- Preliminary estimation of reduction factors in mechanical properties of steel reinforcement due to pitting simulated corrosion
- K. Andisheh ; A. Scott ; A Palermo
- Book Title / Journal: New Zealand Society for Earthquake Engineering (NZSEE) Annual Technical Conference
- Year: 2014 , Volume: , Series:
- Structure types ; Concrete structures
- Keywords: Corrosion ; steel structures
- Description
- In recent years, growing attention has been given to the effects of corrosion on reinforced concrete structures. Marine environment and de-icing salt are two causes chloride-induced corrosion. Basically, there are two types of steel reinforcement
corrosion called general and pitting corrosion. In real corroded reinforced concrete (RC) structures, a mix of the general and pitting corrosion usually takes place. Corrosion decreases the mechanical characteristics of steel reinforcing.
In this study, reduction factors of mechanical properties of steel reinforcement have been estimated through experimental monotonic tensile tests to take into consideration of eccentricity caused by pitting corrosion. Reduction factors have been defined to estimate the effect of corrosion on the reduction in mechanical properties of corroded steel bars. The reduction factors indicate the percentage reduction in the mechanical properties for 1% loss of cross-section area of steel reinforcement.
To meet this aim, pitting corrosion has been simulated by mechanically removing a portion of the cross section form 10mm, steel reinforcement. The reduction factors in terms of yield stress, ultimate stress, module of elasticity and elongation have been estimated from monotonic tensile tests. The relevant deterioration models have been
developed based on the experimental results, and have been used for section-level
analysis of a reinforced concrete bridge pier. The results of section-level analysis show degradation in moment-curvature and force-displacement of the corroded RC bridge pier due to pitting corrosion.
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- Composite slab effects on beam-column subassemblies: Further development
- T. Chaudhari ; G. MacRae ; D. Bull ; G- Chase ; M. Hobbs ; C. Clifton ; S. Hicks
- Book Title / Journal: New Zealand Society for Earthquake Engineering - Annual Technical Conference
- Year: 2014 , Volume: , Series:
- Structure types ; Composite structures
- Keywords: composite slabs
- Description
- Composite slab construction is gaining popularity in New Zealand. These slabs may influence beam column joint subassemblies as they are exposed to earthquakeinduced shaking. However, several design issues with composite slabs need to be addressed so that they can be used to their full advantage in design. These relate to considering the effect of the slab on the beam design strength, the likely statistical variation of the beam and slab under strong seismic shocks that will affect the column joint demand, and the resistance of the panel zone.
In this paper, experimental test setups are described which consider slab isolation, beam
overstrength, full depth slab around the column, low damage connection, and demand on the panel zone. A new concept of slab confinement using a shear key will be presented to form a force transfer mechanism to avoid failure of concrete either in crushing or spalling. Also the development of a non-prying sliding hinge joint low damage connection and its performance with composite slabs is discussed. The outcome of this
will be useful to develop simple design recommendations for the New Zealand steel
standard.
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- Seismic design of composite metal deck and concrete-filled diaphragms - A discussion paper
- K.A. Cowie ; A.J. Fussell ; G.C. Clifton ; G.A. MacRae ; S.J. Hicks
- Book Title / Journal: New Zealand Society for Earthquake Engineering - Annual Technical Conference
- Year: 2014 , Volume: , Series:
- Structure types ; Composite structures
- Keywords: composite deck ; diaphragm
- Description
- One of the most neglected elements in the design of buildings is the horizontal floor diaphragm and its interaction with the lateral load resisting systems. Most multi-story structures depend on the floor slab and roof systems to act as horizontal diaphragms to collect and distribute the lateral loads to the vertical framing members, which provide the overall structural stability.
In steel structures, floor diaphragms are most commonly constructed using composite steel deck with concrete fill, although other systems may also be used. Somewhat surprisingly, given the importance of diaphragms to the overall building response, there is no universally agreed design procedure for determining the diaphragm actions and distribution into the seismic-resisting systems. In addition, the specific issues related to beam design for members collecting lateral loads in composite floor systems has gone largely undocumented.
This discussion paper presents a suggested method in determining the design diaphragm actions at a given floor level, how to proportion their transfer into the seismic resisting systems and how to design and detail the supporting beams/composite metal deck for these actions.
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- Rocking steel shear walls with energy dissipation devices
- G.S. Djojo ; G.C. Clifton ; R.S. Henry
- Book Title / Journal: New Zealand Society for Earthquake Engineering (NZSEE) Annual Technical Conference
- Year: 2014 , Volume: , Series:
- Earthquake engineering
- Keywords: steel shear walls ; energy dissipation devices
- Description
- Conventional steel panel shear walls (SPSWs) comprise thin steel plates framed by beams and columns. These walls have been developed as ductile systems which resist seismic forces through a combination of shear resistance from the plates and flexural resistance from the frames. The internal shear forces in the plates are resolved into diagonal tension and compression principal stresses and after the compression diagonal buckles, the plates behave effectively as tension cross bracing. The ductile action is achieved through tensile yielding of the web plate and a plastic hinge is formed at the beam ends, with the columns expected to remain elastic. Although this system, under severe earthquakes, dissipates considerable energy through the yielding of selected members, structural damage with residual deformation may make repair difficult.
Therefore, an innovative steel panel shear wall is being developed by combining the advantages of the conventional wall system with a centralised rocking mechanism and energy dissipation devices to produce a lateral force resisting system with a low damage design solution that is intended to remain elastic during the rocking and expected to
return to original position after an ultimate limit state level earthquakes. During severe earthquakes, the columns move above or below the original position and the energy dissipation devices provide restoring forces to pull back the columns. A rocking base point at the bottom middle of the wall maintains the stability of the structure. This paper
presents the concept and numerical analysis of this wall focusing on the energy dissipation device system.
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- Development and research of eccentrically braced frames with replaceable active links
- A.J. Fussell ; K.A. Cowie ; G.C. Clifton ; N. Mago
- Book Title / Journal: New Zealand Society for Earthquake Engineering (NZSEE) Annual Technical Conference
- Year: 2014 , Volume: , Series:
- Earthquake engineering
- Keywords: eccentrically braced frames ; steel frames
- Description
- Ductile eccentrically braced frames designed in accordance with the New Zealand Steel Structures Standard, NZS 3404, provide life safety during a design level or greater earthquake; however, the eccentrically braced frame active link may sustain
significant damage through repeated inelastic deformation. This may necessitate postearthquake
replacement of the active link. A bolted replaceable active link can be used to facilitate replacement after a strong earthquake, which reduces repair costs.
New Zealand design guidance for the seismic design of steel eccentrically braced frames was first published in 1995 by the New Zealand Heavy Engineering Research Association within HERA Report R4-76 and has been widely used in practice. This guidance has been recently updated and now includes seismic design procedures for eccentrically
braced frames with replaceable links. This article covers the development and research of eccentrically braced frames with replaceable links. This includes discussions of the comprehensive research programme recently completed in Canada investigating the performance of eccentrically braced frames with replaceable links and finite element analysis undertaken by the New Zealand Heavy Engineering Research Association, to
verify the design procedure for eccentrically braced frames with replaceable links.
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- Experimental studies on cyclic behaviour of steel base plate connections considering anchor bolts post tensioning
- J. Borzouie ; G.A. MacRae ; J.G. Chase ; C.G. Clifton
- Book Title / Journal: New Zealand Society for Earthquake Engineering (NZSEE) Annual Technical Conference
- Year: 2014 , Volume: , Series:
- Earthquake engineering
- Keywords: base plate connections ; experimental study ; seismic performance evaluation
- Description
- This paper presents the experimental tests on cyclic behaviour of the base plate connections that are connected to the foundation with and without fully post tensioned anchor rods. The main aim is to evaluate these connections that are designed with available design procedures from the low damage aspect. Also, the effect of post tensioning on the seismic performance of this type of connection is presented. To characterize the base plate connection damageability, each column base was designed for a particular major inelastic deformation mode such as anchor rod yielding, yielding of the
column, or column and base plate yielding. It is shown that considered joints are not able to be categorized as “a low damage”. Also, post tensioning of the base plate increases the rotational stiffness of the base, and results in more ductility of the column with low axial force.
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- Numerical simulation of shear wall failure mechanisms
- F. Dashti ; R.P. Dhakal ; S. Pampanin
- Book Title / Journal: New Zealand Society for Earthquake Engineering (NZSEE) Annual Technical Conference
- Year: 2014 , Volume: , Series:
- Structural Analysis ; Earthquake engineering
- Keywords: shear walls ; failure mode ; numerical simulation
- Description
- This study investigates the ability of a finite element model in predicting nonlinear behavior and failure patterns of RC structural walls. Experimental results of walls with different shear-span ratios which failed in different modes are used for
verification. The walls are modelled in the finite element analysis program DIANA9.4.4.
Curved shell elements with embedded bar elements are used to simulate the reinforced concrete section of the walls to be analysed. This type of model does not require ‘plane sections to remain plane’ along a wall, and simulates the in-plane axial-flexure-shear
interaction without requiring any empirical adjustment. The model is found to capture the
monotonic and cyclic responses of the tested wall specimens with reasonable accuracy in terms of hysteresis curves and failure patterns. The failure patterns simulated by the model include shear, flexure, flexure-shear and flexure-out of plane modes depending on different parameters particularly shear-span ratio of the specimens. Moreover, the strain profile captured by the model was in good agreement with experimental measurements indicating that in addition to the overall global response predictions, local behaviour of the wall models can be predicted reasonably well.
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- Lateral-force resisting mechanisms of flexure-dominant multi-story structural walls sustained on soft-first-story
- M. Sakashita ; Y. Idosako ; X. Feng ; M Nishiyama
- Book Title / Journal: New Zealand Society for Earthquake Engineering (NZSEE) Annual Technical Conference
- Year: 2014 , Volume: , Series:
- Structural dynamics ; Earthquake engineering
- Keywords: soft story ; lateral force
- Description
- This paper presents lateral-force resisting mechanisms of flexure-dominant multi-story structural walls on a soft-first-story. Two reinforced concrete specimens consisted of the 3-story-high structural wall on the soft-first-story were constructed in 1/3-scale and tested under cyclic loading simulating earthquake motions. The test variable was the longitudinal reinforcement ratio in the boundary beam of the 2nd floor, which was
1.19% or 2.56%. The structural walls yielded in flexure as intended, which, however, did not result in the concentration of deformation only on the 2nd story. The reason is that the boundary beam yielded in flexure and tension, and a yielding mechanism other than intended was formed. The difference in load capacity between the two specimens was not
of significance. The mechanism needed as large drift angle as approximately 2% to attain the design lateral load capacity. The beam-column joints on the 2nd floor failed, which resulted in an inability to sustain the axial load.
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- Investigation of the behaviour of small-scale bridge models using shake table tests
- Z. Chegini ; A. Palermo
- Book Title / Journal: New Zealand Society for Earthquake Engineering (NZSEE) Annual Technical Conference
- Year: 2014 , Volume: , Series:
- Earthquake engineering
- Keywords: shake table testing ; Bridges ; skew angle
- Description
- The skew angle of a bridge is an important boundary condition that affects its behaviour under seismic loading. Although some research has been carried out to identify these effects, such investigations for the most part remain analytical with a few instances including experimental testing. In an effort to understand the effects of skew on the seismic behaviour of bridges, a number of shake table tests have been performed on a skew and a non-skew bridge model and the results have been compared. These smallscale models are representative of two-bay short-span concrete bridges and consist of
precast deck and pier elements which have been assembled using threaded bars. The results of the tests show that although the amount of deck rotation is not higher in the skew deck, this rotation is non-symmetric and may lead to unseating of the deck. It is also discussed that the results of these tests can be used in the design of ‘controlled rocking’ connections in precast bridge structures.
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- Shaking table tests of a base isolated structure with double concave friction pendulums
- F.C. Ponzo ; A. Di Cesare ; D. Nigro ; M. Simonetti ; G. Leccese
- Book Title / Journal: New Zealand Society for Earthquake Engineering (NZSEE) Annual Technical Conference
- Year: 2014 , Volume: , Series:
- Earthquake engineering
- Keywords: shake table testing ; Base Isolation ; SAP2000 ; friction pendulums
- Description
- An extensive experimental seismic testing programme named JETBIS project (Joint Experimental Testing of Base Isolation Systems) has been developed within the RELUIS II project (Task 2.3.2) involving partners from different Italian universities. This paper describes the shaking table test performed by research unit of University of
Basilicata (UNIBAS) on the experimental model with seismic isolators based on Double Concave Friction Pendulum (DCFP). The DCFP isolator contains two separate concave sliding surfaces and exhibits different hysteretic properties at different stages of
displacement response. The experimental model was a 1/3 scaled steel framed structure with one storey and one bay in both directions. Four DCFP bearings with equal properties of the concave sliding surfaces were mounted under each column. The base isolated experimental model was subjected to a set of 7+1 natural earthquakes increasing seismic
intensity in order to achieve the safe displacement of seismic bearings. The main objective of this work is to evaluate the DCFP effectiveness considering different experimental configurations (with both symmetrical and eccentric masses) and different
sliding surfaces conditions (with and without lubrication). A further goal is to verify the reliability of the DCFP isolation system when relevant residual displacements occur due to previous earthquakes. Finally, this paper also shows the experimental testing outcomes compared with the results of non linear time history numerical analyses using SAP2000.
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- Preliminary experimental verification of current content sliding modelling techniques
- T.Z. Yeow ; G.A. MacRae ; R.P. Dhakal ; B.A. Bradley
- Book Title / Journal: New Zealand Society for Earthquake Engineering (NZSEE) Annual Technical Conference
- Year: 2014 , Volume: , Series:
- Earthquake engineering
- Keywords: shake table testing ; friction coefficient
- Description
- Most analytical studies focusing on the sliding of building contents usually make an assumption that the friction force-sliding displacement behaviour is elasto-plastic (e.g. friction coefficient remains constant during sliding). This preliminary study uses experimental data to verify if this assumption is reasonable. Shake table tests of a desk on common flooring materials were conducted to investigate the factors influencing friction behaviour, and to observe the behaviour of the contents under sinusoidal motion. Up to a 15% decrease in friction coefficient was observed with either an 80% increase in mass or a 20 times decrease in relative velocity, indicating that the friction coefficient is dependent on these two parameters. A comparison of the experimental and analytical sliding response of the desk under a single sinusoidal loading pattern on carpet flooring was conducted. Results show that the displacement amplitude of a single sliding excursion and the general sliding trend is well approximated using the elasto-plastic assumption. As such, despite the dependence of friction coefficient on sliding mass and velocity, the elasto-plastic behaviour assumption appears to be reasonable for the sinusoidal loading pattern examined in this paper.
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