Confidence Factor?

Eurocode 8 Part 3 (EC8-3) is devoted to assessment and retrofitting of existing buildings. In order to take into account the uncertainty in the knowledge of structural properties, EC8-3 defines, analogously to the ordinary material partial factors, an adjustment factor, called “confidence factor (CF),” whose value depends on the level of knowledge (KL) of properties such as geometry, reinforcement layout and detailing, and materials. This solution is plausible from a logical point of view but it cannot yet profit from the experience of its use in practice, hence it needs to be substantiated by a higher level probabilistic analysis accounting for and propagating epistemic uncertainty (i.e., incomplete knowledge of a structure) throughout the seismic assessment procedure. This article investigates the soundness of the format proposed in EC8-3. The approach taken rests on the simulation of the entire assessment procedure and the evaluation of the distribution of the assessment results (distance from the limit state of interest) conditional on the acquired knowledge. Based on this distribution, a criterion is employed to calibrate the CF values. The obtained values are then critically examined and compared with code-specified ones. The results pinpoint a number of deficiencies that appear to somewhat invalidate the approach. The methodological significance of the work extends beyond the assessment procedure in EC8-3, since similar factors appear in other international guidelines (e.g., the knowledge factor of FEMA356).     

A Nonlinear Frame Test Structure with Repeatable Behavior for Experimental Dynamic Response History Investigation

This article describes a novel, small-scale nonlinear beam-column connection and an associated six-story frame test structure for the experimental dynamic response investigation of multi-story buildings subjected to earthquake loading. The objective is to create a re-configurable, reusable experimental platform on which several aspects of nonlinear dynamic response can be investigated through successive, exhaustive testing under suites of earthquake records. Static and dynamic calibration tests demonstrate excellent test-to-test repeatability of four structure configurations. These results confirm that the properties of each configuration (period, strength, energy dissipation) remain invariant, thus allowing future experimental investigations (e.g., of peak engineering demands) under earthquake loading.     

Closure to the Discussion of “Full-Scale Experimental Verification of Soft-Story-Only Retrofits of Wood-Frame Buildings using Hybrid Testing” by Bruce Maison

The authors of the article “Full-Scale Experimental Verification of Soft-Story-Only Retrofits of Wood-Frame Buildings using Hybrid Testing” respond to a discussion by Bruce Maison.     

Impact of Vertical Ground Excitation on a Bridge with Footing Uplift

Ground motions recorded in the epicentral region of an earthquake often have a strong vertical component with dominant high frequencies. Damage to bridges in near-source regions due to strong vertical ground motion has been reported. The beneficial effects of footing uplift on structural performance in form of reduction of seismic response of structural members have been confirmed in previous research. The uplift of bridge piers has been utilised in a very limited number of bridge structures, e.g., the South Rangitikei railway bridge in New Zealand. However, the near-fault seismic behaviour of bridges with footing uplift has been even less addressed. In this study shake table investigations were carried out on the response of a single-span bridge model with footing uplift subjected to simultaneous vertical and horizontal excitations. Near-fault ground motions recorded in the Canterbury earthquake sequences of 2010 and 2011 were used. The experimental results show that inclusion of vertical ground motions produce stronger axial force in the pier and larger bending moment in the deck. Concurrent horizontal and vertical excitations may also cause more frequent footing uplift than the solely horizontal excitations.     

甘肃武威出土铜奔马铸造工艺初探

甘肃武威出土的东汉铜奔马和铜车马仪仗队是我国古代青铜艺术品中罕见的杰作,是中国众多文物中的代表和古老中华文明的一种象征。甘肃省博物馆通过现代科学仪器检测及综合分析发现:铜奔马和铜车马仪仗队都是陶范铸造法铸造而成,而不是失蜡法铸造的;铜奔马铸造时在铜质马腿内夹铸了卯榫状铁芯骨,以增强马腿的强度和支撑力;铜车马仪仗队中甲型马和刻有铭文的乙型马,是铸造工艺不同的两批制品。这些发现对进一步研究铜奔马及墓主人提供了新的材料。     

Combined In-Situ and Laboratory Minor Destructive Testing of Historical Mortars

ABSTRACT

Mortar is of all masonry components the most difficult to be experimentally characterized in heritage buildings. This article investigates the possibility of combining different in-situ and laboratory minor destructive testing (MDT) techniques to assess the strength of mortar in historical brickwork. Lime mortar and clay brick walls were built in the laboratory and then tested in order to derive empirical correlation rules among three different MDT techniques: double punch test (DPT), helix pull-out test (HPT), and pin penetration test (PPT). The outcomes of this activity were used eventually to assess the mortar properties of an important historical heritage structure, Casa Puig i Cadafalch, located near Barcelona. The research is intended to promote the use of MDT in studies and conservation works on built cultural heritage by providing criteria for the evaluation of the strength of existing mortar with respectful sampling and testing techniques.     

Shaking Table Tests of a Structure Equipped with Superelastic Dampers

The energy dissipation capacity of the NiTi alloy was evaluated as part of a series of shake table tests. A superelastic damper was developed to take advantage of the hysteretic energy dissipation associated with this type of shape memory alloy. Each device was tested at different intensity levels. A vertical steel cantilever with 600 kg mass on top was subjected to a series of ground motions with different spectral characteristics. The dampers were placed as part of a tie system, restraining the horizontal movement of the top mass. The devices showed stable hysteretic behavior allowing for energy dissipation.     

The Commonwealth and South Africa: From Smuts to Mandela

The creation of modern South Africa as an independent unitary state within the British Empire (c. 1910) gave birth to the Commonwealth idea. Jan Smuts’s views on Commonwealth were formative and they continued to inform the evolution of the organisation until the end of the Second World War. Also significant was the role played by Afrikaner nationalist leader J. B. M. Hertzog, who exerted a critical influence on the 1926 Balfour Declaration and Statute of Westminster. At the point of South Africa’s departure from the Commonwealth in 1961, the Commonwealth divided between new entrants, who cast South Africa as a pariah, and older member states who lamented the exit of a troubled family member. Even after South Africa’s departure from the Commonwealth in 1961, apartheid’s significance as the global exemplar of institutionalised racism and colonial rule helped to bind the Commonwealth as a multi-racial organisation with strongly defined ethical values. South Africa’s reintegration in 1994, with Nelson Mandela to the fore, was welcomed as a triumph for the Commonwealth. Paradoxically, however, this proved a pyrrhic victory and may actually have contributed to the Commonwealth’s state of indirection.     

Intercontinental Hybrid Simulation for the Assessment of a Three-Span R/C Highway Overpass

This paper presents hybrid simulations of a three-span R/C bridge among EU, US, and Canada. The tests involved partners located on both sides of the Atlantic with each one assigned a numerical or a physical module of the substructured bridge. Despite the network latency in linking remote sites located on the two sides of the Atlantic the intercontinental hybrid simulation was accomplished and repeated successfully, highlighting the efficiency, and repetitiveness of the approach. Adaptations, challenges, and limitations are discussed, focusing on the implications of network communication latency, the insensitivity of the sub-structuring arrangement, and the accuracy of the results obtained.