Seismic Site Response of A Large Deep-seated Rock Slope Revealed by Field Monitoring and Geophysical Methods

Shidaguan Slope (hereinafter short for SDG Slope) is an unstable rock slope with an area of 30.78×104 m2 and a deformation depth of 30-70 m in Maoxian County, Sichuan Province, China. Three seismometers (P2-P4) with high sensitivity were installed at different locations on the unstable part of the slope. P2 and P3 were almost at the same elevation (2221 m and 2247 m), while P4 was the lowest (at 2140 m). Another seismometer (P1) sat in a stable location at a higher elevation (2373 m). 99 shallow earthquakes were analyzed. According to the peak acceleration ratios of three seismometers (P2-P4) on the unstable part and another seismometer (P1) on the stable part, the points at lower elevations showed greater seismic amplification (with the amplification coefficient of 2.64-3.51) than one at a higher elevation. And points at relatively thinner part (23 m thick) of unstable slope showed greater seismic amplification than ones at thick part (60-75 m thick). The same rule was also found in studying the site-epicenter azimuth and earthquake magnitude data. Based on the relationship between amplification coefficient and resistivity and rock core, the seismic response amplification was affected by the lithofacies difference. The lithofacies with resistivity values of 50-100 Ohm.m and RQD values of 0-50 % incurred seismic response amplification, which was restrained by the below lithofacies with resistivity values of 10-50 Ohm.m and ROD values of 0 %. When building on slope areas, the lithofacies difference should be taken into full consideration.

Direct generation of floor design spectra (FDS) from uniform hazard spectra (UHS) — Part I: formulation of the method

In most current building codes, seismic design of non-structural components (NSCs) is addressed through empirical equations that do not capture NSC response amplification due to tuning effects with higher and torsional modes of buildings and that neglect NSC damping. This work addresses these shortcomings and proposes a practical approach to generate acceleration NSC floor design spectra (FDS) in buildings directly from their corresponding uniform hazard spectra (UHS). The study is based on the linear seismic analysis of 27 reinforced concrete buildings located in Montréal, Canada, for which ambient vibration measurements (AVM) are used to determine their in situ three-dimensional dynamic characteristics. Pseudo acceleration floor response spectra (PA-FRS) are derived at every building floor for four different NSCs damping ratios. The calculated roof FRS are compared with the 5% damped UHS and a formulation is proposed to generate roof FDS for NSCs with 5% damping directly from the UHS.

Response amplification of back-rotated piles

Piles are largely back-rotated in sliding slope or subjected to lateral spreading. This paper reveals for the first time that response of these piles (e.g., displacement, rotation, bending moment, and shear force) is amplified against forward rotating piles. In particular, magnification is detrimental, once normalized rotational stiffness (NRS) of the piles is around a singularity value (i.e., normalized singularity stiffness, NSS). New expressions are developed to gain the NSS value, the magnification degree, and the sliding depth to incur the singularity. The NRS is assessed using 1g model tests. The solutions are adopted to capture the response of the model piles, to detect new failure mechanism of Showa Bridge, and to check the safety of Christchurch bridges. The main conclusions are as follows: (i) piles are prone to response amplification, when subjected to lateral spreading or in sliding slopes. (ii) The NRS is only slightly affected by soil movement profiles and sliding depths. (iii) Showa Bridge collapsed from displacement amplification of back-rotated piles. Finally, (iv) the roller connections between girder and piers, and an integral abutment and piers are proved to be effective to curb the amplification. The amplified response needs to be assessed in practice to lessen failure of back-rotated piles.

Assessment of Accidental Torsion in Building Structures Using Static and Dynamic Analysis Procedures

This article presents the findings of a study on assessment of the increase in building’s response due to accidental torsion when subjected to seismic forces. Critical stiffness and geometrical parameters that define buildings torsional response are examined including: (1) the ratio, Ω, between uncoupled torsional frequency ωθ to uncoupled translation frequencies in the direction of ground motion ωx or ωy, (2) floor plan aspect ratio, b/r, which is a function of the floor dimension and radius of gyration. The increased response is assessed on symmetric multi-storey buildings using both static and dynamic analysis methods specified by ASCE-7 and considering parameters affecting the torsional response. It was concluded that static and dynamic analysis procedures predict different accidental torsion responses. Static analysis based on the Equivalent Lateral Force (ELF) method predicts more conservative accidental torsions responses for flexible structures with Ω < 0.7~0.80, while the responses are less conservative for stiffer buildings. The conservativism in static analysis method is attributed to the response amplification factor, Ax. Floor plans and their lateral support system having frequency ratio Ω = 1 will also have a torsional radius equal to radius of gyration, and will experience drop in torsional response relative to more torsionally flexible buildings. This article presents a procedure to overcome the shortcomings of static and dynamic analysis procedures in terms of estimating accidental torsion response of symmetric building structures.

Hearing Aid Self-Adjustment: Effects of Formal Speech-Perception Test and Noise

While listening to recorded sentences with a sound-field level of 65 dB SPL, 24 adults with hearing-aid experience used the “Goldilocks” explore-and-select procedure to adjust level and spectrum of amplified speech to preference. All participants started adjustment from the same generic response. Amplification was provided by a custom-built Master Hearing Aid with online processing of microphone input. Primary goals were to assess the effects of including a formal speech-perception test between repeated self-adjustments and of adding multitalker babble (signal-to-noise ratio +6 dB) during self-adjustment. The speech test did not affect group-mean self-adjusted output, which was close to the National Acoustics Laboratories’ prescription for Non-Linear hearing aids. Individuals, however, showed a wide range of deviations from this prescription. Extreme deviations at the first self-adjustment fell by a small but significant amount at the second. The multitalker babble had negligible effect on group-mean self-selected output but did have predictable effects on word recognition in sentences and on participants’ opinion regarding the most important subjective criterion guiding self-adjustment. Phoneme recognition in monosyllabic words was better with the generic starting response than without amplification and improved further after self-adjustment. The findings continue to support the efficacy of hearing aid self-fitting, at least for level and spectrum. They do not support the need for inclusion of a formal speech-perception test, but they do support the value of completing more than one self-adjustment. Group-mean data did not indicate a need for threshold-based prescription as a starting point for self-adjustment.

"Autopista Urbana Siervo de la Nación" - Flyover at México City Lake Zone: The importance of design to achieve a sustainable infrastructure during ist life-cycle

<p>The “Autopista Urbana Siervo de la Nación” (AUSN) Highway, is located at Mexico City, and is currently under construction. The highway, with a length of 14.5Km and 4 lanes divided in 2 carriageways (A4 type cross section), intends to target the milestone of a fast and safe road axis. The available right-of-way to built the new infrastructure presents several restrictive constrains that led to the construction of a flyover throughout approx. 90% of the AUSN total length.</p><p>The unique geotechnical scenario that characterizes the Valle de México’s lake zone, with the well- known regional settlement phenomena, along with the peculiar features that define the seismic action within the “lacustres” areas of the city, associated with high structural response amplification, lead to complex structural solutions and demanding calculations, particularly concerning the foundation´s design, optimizing the structure behaviour and minimizing the global costs during all the infrastructure’s life cycle.</p>

A Sensitivity Based Heuristic for Optimal Blade Arrangement in a Linear Mistuned Rotor

This paper investigates methodologies for finding optimal or near-optimal blade arrangements in a bladed disk with inserted blades for minimizing or maximizing blade response amplification due to mistuning in material properties of the blades. The mistuning in the blades is considered to be known, and only their arrangement is modifiable. Hence, this is a problem in discrete optimization, particularly combinatorial optimization where the objective of response amplification is a nonlinear function of the blade arrangement. Previous studies have treated mistuning as a continuous parameter to analyze its effects on the response amplification. Sensitivity metrics have proven to be an important tool in quantifying the effects of mistuning. One such sensitivity metric is used here to formulate an iterative heuristic approach to solve the optimization problem. A component mode mistuning reduced order model is used for fast evaluations of the dynamic responses of a bladed disk with a given blade arrangement. At any iteration the sensitivity of the maximum response of the current rotor design to changes in blade stiffnesses due to changes in the blade arrangement is used to predict the arrangement for the following iteration. In addition to the proposed sensitivity-based approach, we use genetic algorithms to find optimal arrangements and compare results with the heuristic approach.