1、AN-04-2-2 Static Testing of Seismic Restraint Devices Paul W. Meisel, P.E. Member ASHRAE ABSTRACT In support of the design process, manufacturers of seismic components typically perform tests to document the capacity of these devices. A test requirement or acceptance criterion is not clearly defined
2、 by the building codes. In line with their charge of ensuring code compliance, OSHPD (Ofice of State- wide Health Planning and Development, California) has developed the primary static anchorage evaluation “stan- dard” in use today. However, because it links directly back to the California Building
3、Code requirements, this standard is not necessarily appropriate to the requirements of other jurisdic- tions. ASHRAE and VISCMA (Vibration Isolation and Seismic Control Manufacturers Association) are currently working to develop new uniform static testing standards that address the wide range of app
4、lications and code requirements throughout the United States to bring a higher level of consistency to the industry. This paper reviews the history of seismic qualijkation, pros and cons of the current requirements, development of an appropriate industry standardfor static testing of components, tes
5、t methods, failure criteria, and a common format for the presentation of the data collected. HISTORY Prior to 1980, apart from the nuclear industry, there were no significant standards for the certification of equipment restraint componentry. Component manufacturers, in support of the design process
6、, performed the only analysis or compo- nent testing done for noncritical applications. Because of the lack of a recognized standard, these evaluation methods tended to be highly inconsistent. In 1977, the Onice of Statewide Health Planning and Development, California (OSHPD) was formed when the for
7、mer Department of Health was broken down into smaller agencies. Californias Hospital Facilities Seismic Safety Act of 1983 took the enforcement of the California Building Code (CBC), as it applied to hospitals and many health care facili- ties, away from local jurisdictions and put it under the auth
8、or- ity of OSHPD. As part of the act, Section 129895 requires OSHPD to develop and maintain standards and test criteria for equipment anchorage consistent with CBC requirements. Basic test provisions were developed, introduced, and are being used today with good success. The static test results are
9、also more broadly applicable as an indicator of a restraint components ability to resist seismic forces. An option in the above section allows manufacturers, designers, or suppliers of equipment anchorage systems to provide sufficient data for OSHPD to evaluate the anchorage system. Because of its r
10、educed subjectivity, testing has been adopted by most manufacturers of restraint components as being an expedient method of obtaining ratings for the restraint devices themselves. For the direct attachment of restraint components to the structure, design load factors for relatively ductile bolted or
11、 welded connections are currently well defined and well docu- mented. With respect to concrete anchorage, however, the allowable load factors are not as well defined. Because of the minimal ductility of the concrete connection, a one-time pull test rating is not a suitable rating system for a dynami
12、c load condition such as a seismic event. Significant efforts have been made of late to generate reasonable seismic load capacity factors by ICBO (Interna- tional Conference of Building Officials), AC1 (The American Paul Meisel is vice president of engineering at Kinetics Noise Control, Inc., Dublin
13、, Ohio. 02004 ASHRAE. 329 Concrete Institute), and SEAOSC (Structural Engineers ASSO- ciation of Southern California). Currently, ICBO has three separate “AC” (Acceptance Criteria) documents (AC0 1, AC58, and AC193) that address testing methods and evalua- tion of concrete and masonry anchorage for
14、various anchor types. ACI Code 355.2-00 provides test and evaluation criteria for post-installed anchors in concrete and a newer AC1 Code 3 18-02, in particular Appendix D, offers a more stringent eval- uation criteria that is expected to replace 355.2-00. AC1 Code 355.2-00 is included by reference
15、in ICBO AC193. Lastly, SEAOSC developed the Standard Method of Cyclic (Reversed) Load Test for Anchors in Concrete or Grouted Masonry in 1996/1997. The procedures in this docu- ment are referenced in ICBO AC01 and AC58. Unfortunately, anchors are not readily available that have been qualified to the
16、 above (at the time of this writing, I do not know of any). The main problem is that although the various manufacturers have extensively tested anchors, the tests are different from each other and, in most cases, different from the more recently developed criteria identified above. This is particula
17、rly true of dynamic and cracked concrete qualifica- tions. The various anchor manufacturers are working toward developing a common set of standards that is consistent with the above requirements, but this has not yet been accom- plished. In lieu of having fully qualified anchors, current anchor allo
18、wables are drawn from ICBO ER (evaluation report) data. These data do not involve dynamic or damaged concrete factors, but the final rating does include a significant safety factor. While the building code enforcement agencies currently use this basic information, the interpretations of the allowabl
19、e anchor loads drawn from the documents vary under some jurisdictions. When evaluating the anchorage of seismic restraint devices, many factors need to be addressed. First, the same restraint component can be anchored in a number of different ways (anchored to concrete, bolted with through bolts, we
20、lded, or screwed into timber). The variation in the capacity of this connection must be evaluated for each specific case. This is further augmented by the state of flux of allowable anchor capacities. Because of these variables and an inability to repeatedly duplicate concrete anchor capacities in a
21、 restraint component test, the anchorage connection has histor- ically been computed. Fortunately, even relatively complex bolted, screwed, or welded connections to the structure are relatively simple to analyze. The capacity of a restraint is then determined to be the lessor of the computed anchora
22、ge capacity or the tested restraint component capacity. TRADE-OFFS BETWEEN STATIC AND DYNAMIC TESTING PROCEDURES With the advent of the IBC, there has been a considerable push toward dynamically testing equipmendrestraint combi- nations. ICBO has developed a standard (AC150 that defines procedures t
23、o accomplish this. Although this has long been a requirement in the nuclear industry, because of the lesser sensitivity, volume of components involved, cost, and sched- uling issues, it has not been required for other applications until recently. With this type of test, a piece of equipment is mount
24、ed to a shaker plate and subjected to one or several recorded earthquake spectra whose amplitude has been factored to closely match the design requirements at the project site. This test has the potential for catching failures that might be caused by resonant vibrations or impact loads within the eq
25、uipmendrestraint system, but it cannot be easily trans- lated from one arrangement to another. The cost of this type of test is usually prohibitive for a typical job. With respect to the reliability of the equipment itself, a dynamic test may be the most accurate qualification method. The myriad of
26、components involved and the responses of the various subsystems to vibrations would be very difficult to mimic analytically, and a static test will not strain any internal mechanical components. To properly evaluate the internal effects that result from impact loads generated in the snubbing element
27、 in an isolated system, testing must be performed either with the restraints/isolators selected for use in the field or with a snubbing system that performs in a similar manner. However, the above is not true of the restraintlanchorage system. For these systems, the load paths are simple and straigh
28、tforward. There are no resonant or harmonic issues that have a significant impact. The central premise required to ensure consistent performance of these components is that both the structure on which the equipment is mounted and the equipment (or frame) being supported is rigid enough to with- stan
29、d the imposed loads without undo distortion or failure. A relatively tight definition of internal clearances, snubbing pad parameters, and allowed housing deformation within the restraint elements will ensure that the dynamic loads gener- ated as a result of impact forces would be quite consistent b
30、etween various manufacturers or types of restraints. This consistency allows development of an appropriate “impact” factor that can be applied to a simple static analysis, eliminat- ing the need to test every systemhestraint combination. In addition, during the analytical process of sizing the restr
31、aint components for particular applications, the deter- mined peak vertical and horizontal loads at all restraint loca- tions better support the ability of the structural engineer of record to confirm that the structure can withstand these loads. Likewise, using these same loads, the attachment poin
32、ts on the equipment can easily be analyzed or tested to ensure conform- ance by the equipment or support frame manufacturer. Currently included in the design force calculations are factors to account for impact on the restraint, as well as reduced anchorage allowables for inconsistencies in the anch
33、or/concrete/installation interface. A reasonable match between actual performance and these impact factors occurs if the restraint housing is assumed rigid, a clearance offering 330 ASHRAE Transactions: Symposia M.25 in. motion is maintained, and a *0.25 in. thick elasto- meric snubbing element is u
34、sed. Although restraint housings are required to be ductile, current practice is to include a global safety factor of 2: 1 in the load rating based on their statically tested capacity. This factor is adequate to address short-term fatigue and strain relief issues when comparing the static value to d
35、ynamic load condi- tions. This combination of test criteria and load factoring as dictated in the seismic load derivation process ensures the validity and conservative nature of the static testing and rating procedure. The ability to use static load ratings when selecting restraint systems (versus d
36、ynamic testing) greatly reduces project-specific test costs. CURRENT STATIC TESTING STANDARD (OSHPD) The restraint testing procedure used today requires that restraints be loaded vertically in tension and compression as well as horizontally on both major axes. In addition, most components are also t
37、ested with combined equal tensile and lateral loads applied along the major axes. The current test requirement as identified in the OSHPD pre-approval test procedure is that restraints will be tested to 1.5 times the rated dead load plus 2.0 times any applicable live load plus 2.0 times the applicab
38、le seismic load without failure. Detailed failure criteria and a test procedure as defined by the test applicant are to be provided to OSHPD prior to beginning the testing program. If the proposed tests and failure criteria are accept- able to OSHPD, the applicant is granted approval to begin the te
39、st program. Using the currently defined OSHPD procedure as a national standard, however, has some drawbacks. First, the lack of clearly defined test procedures and failure criteria has forced applicants to take a best “guess” as to what OSHPD is looking for. Variations in interpretation by applicant
40、s have generated variations in the procedures and criteria used to define failure. In working to define a more unified test stan- dard, the various manufacturers that are involved in ASHRAE and VISCMA committees have found that while the test procedures submitted to OSHPD by the various organization
41、s were quite similar, the definition of failure differed consider- ably. The net result is that nearly identical restraints, both tested to criteria acceptable to OSHPD, could conceivably carry very different capacity ratings. An additional shortfall of the OSHPD documentation procedure is that the
42、ratings that result from the tests, partic- ularly for restraints anchored to concrete, are based on allow- able anchor loads more restrictive than those mandated for less sensitive applications or in less seismically active areas of the country. While these values are not inappropriate for hospital
43、 or other “life safety” applications, they tend to be excessive for these other more conventional applications. The direct result is that the published OSHPD restraint capacity rating is conservative for most applications. If using these ratings to meet the local seismic load requirement under diffe
44、rent circumstances, a more cumbersome and more expensive restraint than might otherwise be required would be selected. Lastly, OSHPD is a government agency and, along with other agencies (especially in California), has been subject to severe budget limitations. As a result, timeliness in processing
45、approvals often becomes a problem. ALTERNATE TESTING STANDARDS At present, there is one dynamic standard that has been developed and two alternate static testing standards that are being developed. As mentioned previously, ICBO has devel- oped the AC 156 acceptance criteria. This is basically a shak
46、e table test of the entire equipmentlrestraint system. A dynamic test such as AC156 is necessary to evaluate the internals of sensitive or fragile equipment, particularly in applications where the continued functioning of that equipment is required. This, however, is often impractical for testing re
47、straint devices. It should be noted that while AC 156 can be used to eval- uate the performance of attachment restraint devices, the actual anchorage (particularly to concrete) must be evaluated analytically. This is because the required anchorage de-ration factors are extremely difficult to mimic u
48、nder test conditions. It should also be noted that past experience with restraint components indicates that properly sized components (based on static evaluations) rarely fail. Instead, it is the impact of the pounding on the equipment itself or on the anchorage that is the primary culprit. With reg
49、ard to the anchorage, as it is really not considered during the test, AC156 can do very little. However with respect to the equipment durability, it has the potential to do a lot. Past treatment of most equipment in the various building codes has been to address them as “black boxes.” This meant that as long as the equipment was restrained, it didnt matter what happened inside of it. Out of this came experience that has shown some pieces of equipment to be fragile, frequently suffering seismic internal damage, and other equipment to be durable, rarely suffering seismic internal damage. A pr
