Empirical Evidence for Site Coefficients in Building Code Provisions

2002 ◽  
Vol 18 (2) ◽  
pp. 189-217 ◽  
Author(s):  
Roger D. Borcherdt
Keyword(s):  
Confidence Level ◽  
Empirical Data ◽  
Site Response ◽  
Building Code ◽  
Northridge Earthquake ◽  
Empirical Estimates ◽  
Site Coefficients ◽  
Percent Confidence Level ◽  
Lower Confidence Bound ◽  
Code Provisions

Site-response coefficients, Fa and Fv, used in U.S. building code provisions are based on empirical data for motions up to 0.1 g. For larger motions they are based on theoretical and laboratory results. The Northridge earthquake of 17 January 1994 provided a significant new set of empirical data up to 0.5 g. These data together with recent site characterizations based on shear-wave velocity measurements provide empirical estimates of the site coefficients at base accelerations up to 0.5 g for Site Classes C and D. These empirical estimates of Fa and Fv as well as their decrease with increasing base acceleration level are consistent at the 95 percent confidence level with those in present building code provisions, with the exception of estimates for Fa at levels of 0.1 and 0.2 g, which are less than the lower confidence bound by amounts up to 13 percent. The site-coefficient estimates are consistent at the 95 percent confidence level with those of several other investigators for base accelerations greater than 0.3 g. These consistencies and present code procedures indicate that changes in the site coefficients are not warranted. Empirical results for base accelerations greater than 0.2 g confirm the need for both a short- and a mid- or long-period site coefficient to characterize site response for purposes of estimating site-specific design spectra.

PCI Standard Design Practice Ref ACI 318-14

2021 ◽  
Author(s):  
Keyword(s):  
Prestressed Concrete ◽  
Precast Concrete ◽  
Building Code ◽  
Design Practice ◽  
Structural Concrete ◽  
Design Engineers ◽  
Standard Design ◽  
Precast Prestressed Concrete ◽  
Consistent Approach ◽  
Code Provisions

Precast, prestressed concrete design is based on conformance with the provisions of the American Concrete Institute’s (ACI’s) Building Code Requirements for Structural Concrete (ACI 318-14) and Commentary (ACI 318R-14). In most cases, these provisions are followed explicitly. Occasionally, interpretation of some sections of ACI 318 is required to ensure quality is maintained in conjunction with the unique characteristics of precast and prestressed concrete fabrication, shipping, and erection. Members of the PCI Building Code Committee, along with other experienced precast concrete design engineers, have identified code provisions, detailed in this publication, that require clarification or interpretation. These design practices are followed by most precast concrete design engineers to produce safe, economical precast concrete structures and they provide a consistent approach for the designers and contractors.

Eccentricity in irregular multistory buildings

1986 ◽  
Vol 13 (1) ◽  
pp. 46-52 ◽  
Author(s):  
V. W.-T. Cheung ◽  
W. K. Tso
Keyword(s):  
Dynamic Analysis ◽  
Necessary Conditions ◽  
Vertical Axis ◽  
Building Code ◽  
Necessary Condition ◽  
Practical Procedure ◽  
Multistory Buildings ◽  
Plane Frame ◽  
Code Procedure ◽  
Code Provisions

To evaluate the seismic torsional effect on multistory buildings, the concept of eccentricity is extended from single-story buildings to multistory buildings by defining the locations of the centers of rigidity at each floor. A practical procedure to locate the centers of rigidity and hence floor eccentricity is introduced. This procedure depends on the use of plane frame computer programs only and is suitable for use in design offices. The seismic torsional provisions in the National Building Code of Canada 1985 (NBCC 1985) explicitly emphasize that the code provisions apply to buildings where the centres of rigidity lie on a vertical axis only. By means of examples, it verifies the claim of NBCC 1985. Also, it shows that, for buildings with centers of rigidity scattered from a vertical axis, the code procedure may or may not apply. Therefore, one should interpret the condition of centers of rigidity located along a vertical axis to be a sufficient, but not a necessary, condition for the NBCC 85 code provisions to be applicable. Until the necessary conditions are known, dynamic analysis remains the most reliable method to assign the torsional effects to various portions of the building. Key words: building code, center of rigidity, dynamic analysis, eccentricity, irregular, multistory, seismic, torsion.

Directional topographic site response at Tarzana observed in aftershocks of the 1994 Northridge, California, earthquake: Implications for mainshock motions

1996 ◽  
Vol 86 (1B) ◽  
pp. S193-S208 ◽  
Author(s):  
Paul Spudich ◽  
Margaret Hellweg ◽  
W. H. K. Lee
Keyword(s):  
Site Response ◽  
Aftershock Sequence ◽  
Northridge Earthquake ◽  
Factors Affecting ◽  
Soil Response ◽  
Amplification Ratio ◽  
East End ◽  
A Site ◽  
The Hill ◽  
East West

Abstract The Northridge earthquake caused 1.78 g acceleration in the east-west direction at a site in Tarzana, California, located about 6 km south of the mainshock epicenter. The accelerograph was located atop a hill about 15-m high, 500-m long, and 130-m wide, striking about N78°E. During the aftershock sequence, a temporary array of 21 three-component geophones was deployed in six radial lines centered on the accelerograph, with an average sensor spacing of 35 m. Station C00 was located about 2 m from the accelerograph. We inverted aftershock spectra to obtain average relative site response at each station as a function of direction of ground motion. We identified a 3.2-Hz resonance that is a transverse oscillation of the hill (a directional topographic effect). The top/base amplification ratio at 3.2 Hz is about 4.5 for horizontal ground motions oriented approximately perpendicular to the long axis of the hill and about 2 for motions parallel to the hill. This resonance is seen most strongly within 50 m of C00. Other resonant frequencies were also observed. A strong lateral variation in attenuation, probably associated with a fault, caused substantially lower motion at frequencies above 6 Hz at the east end of the hill. There may be some additional scattered waves associated with the fault zone and seen at both the base and top of the hill, causing particle motions (not spectral ratios) at the top of the hill to be rotated about 20° away from the direction transverse to the hill. The resonant frequency, but not the amplitude, of our observed topographic resonance agrees well with theory, even for such a low hill. Comparisons of our observations with theoretical results indicate that the 3D shape of the hill and its internal structure are important factors affecting its response. The strong transverse resonance of the hill does not account for the large east-west mainshock motions. Assuming linear soil response, mainshock east-west motions at the Tarzana accelerograph were amplified by a factor of about 2 or less compared with sites at the base of the hill. Probable variations in surficial shear-wave velocity do not account for the observed differences among mainshock acceleration observed at Tarzana and at two different sites within 2 km of Tarzana.

Design for seismic torsional forces

1984 ◽  
Vol 11 (2) ◽  
pp. 150-163 ◽  
Author(s):  
J. L. Humar
Keyword(s):  
Ground Motion ◽  
Analytical Study ◽  
Critical Evaluation ◽  
Building Code ◽  
Rotational Ground Motion ◽  
Building Model ◽  
Design Basis ◽  
Building Models ◽  
Adequate Design ◽  
Code Provisions

An analytical study of the responses of a single storey and a multistorey building model to a combined translational and rotational ground motion is presented. The models, which are assumed to be elastic, are eccentric about one plan direction but are symmetric about the perpendicular direction. The ground excitations are represented by idealized spectra.A critical evaluation is made of the torsion provisions of the National Building Code of Canada. It is shown that the code provisions, while not necessarily nonconservative, are somewhat difficult to apply for multistorey buildings. An alternative provision for design eccentricity is proposed. The forces obtained by the use of the proposed method are compared with the analytical results of single storey and multistorey building models and are shown to provide an adequate design basis.

scholarly journals Facilities Planning for Safety and Emergency Response: Bridging the Gap between Design Features and Safety Planning

2013 ◽  
Vol 56 (1) ◽  
pp. 17-28
Author(s):  
Steve Schultz ◽  
Jack Paul
Keyword(s):  
Emergency Response ◽  
Building Construction ◽  
Building Code ◽  
Safety Planning ◽  
Design Features ◽  
Safe Operation ◽  
Facilities Planning ◽  
Safety Considerations ◽  
Code Provisions ◽  
Design And Construction

This article describes some of the safety considerations for the design and construction of micro/nano facilities and applicable building code provisions. The two key elements required for safe operation in micro and nanotechnology facilities are: (1) engineered features incorporated into building construction, and (2) administrative features that deal with how people work within the facility.

scholarly journals Digital Promise COVID-19 Student Survey Topline Data Report

2020 ◽  
Author(s):  
◽  
Keyword(s):  
Confidence Level ◽  
Sampling Error ◽  
National Sample ◽  
Student Survey ◽  
Full Sample ◽  
Percent Confidence Level ◽  
Part Time Students ◽  
Part Time ◽  
Stem Students ◽  
College Or University

This Digital Promise survey was conducted May 13-June 1, 2020, among a random national sample of 1,008 full- or part-time students enrolled in a two- or four-year college or university who were taking in-person or blended for-credit courses before the coronavirus outbreak began that then transitioned to remote instruction. The sample includes 620 students who took a STEM course that transitioned completely online. Results have a margin of sampling error of 3.6 points for the full sample, 4.6 points among students who took a STEM course, and 5.8 points among those who did not take a STEM course. Error margins are larger for subgroups. At a 50/50 division of opinion, a difference of 8 points between STEM and non-STEM students is needed for significance at the 95 percent confidence level.

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