Using the HP Tie-Down Option Kit for seismic anchoring of HP 10000 G2 series racks

best practices

Abstract.............................................................................................................................................. 2 Introduction......................................................................................................................................... 2 HP Tie-Down Option Kit........................................................................................................................ 3 Anchoring methods.............................................................................................................................. 5

Anchoring in solid concrete (ground floor) .......................................................................................... 5 Anchoring in concrete fill over a metal deck (upper floor) ..................................................................... 6 Anchoring in a raised floor system ..................................................................................................... 6

Seismic hazard locations ...................................................................................................................... 7 Anchor design requirements................................................................................................................ 10 Appendix A: Seismic load calculations for HP 10642 rack..................................................................... 14 Appendix B: HP 10000 G2 series physical properties ........................................................................... 20 Appendix C: Tie-Down kit development information ............................................................................... 21 For more information.......................................................................................................................... 22 Call to action .................................................................................................................................... 22

Abstract Equipment racks are typically shipped with only basic provisions for stabilization. Rack installations in geographical areas that present a risk of seismic activity require special consideration by data center installation architects. This paper describes an HP solution for anchoring HP 10000 Generation 2 (G2) series equipment racks to avoid damage or serious injury in the event of building or floor movement. It provides engineering drawings, parameters, and calculations to help customers determine how to maximize rack stability in their computing facilities. This paper assumes familiarity with seismic terms and measurements.

Introduction HP 10000 G2 Series equipment racks are available in multiple sizes (Figure 1) to meet specific customer requirements. Each rack is shipped with leveling feet and casters that are adequate for installation in non-seismic locations. However, rack installation in some geographical locations may require further consideration. A floor that shakes or moves due to severe vibrations or seismic activity can be catastrophic to personnel if heavy equipment is allowed to roll, slide, or fall.

Figure 1. HP 10000 G2 Series racks

42U 47U 36U 22U

To address potential seismic conditions and to prevent sliding, tipping, or falling, the rack should be secured to the floor using the HP Tie-Down Option Kit.

NOTE The HP Tie-Down Option kit is designed to prevent injury to personnel and minimize equipment damage during seismic activity. It is assumed that the rack and equipment installed in the rack are not required to remain functional following a seismic event.

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HP Tie-Down Option Kit The HP Tie-Down Option Kit is designed for anchoring HP 10000 G2 Series racks in sizes up to 47U to meet building code guidelines in locations where seismic activity should be considered. Each kit includes front and rear hold down brackets and mounting hardware. The brackets attach to an HP 10000 G2 rack as shown in Figure 2. Each bracket is attached to the rack using four alloy steel, quenched and tempered M8x20mm bolts. The two brackets work together primarily to constrain front-to-rear rack moments.

NOTE The term “moment” as used in this document refers to force or motion caused by seismic activity.

Figure 2. HP Tie-Down Option Kit installation

Front hold down bracket installation (viewed from front)

HP 10642 Rack with kit installed Rear hold down bracket installation (viewed from rear)

NOTE Detailed installation instructions for the HP Tie-Down Option Kit are available in the HP 10000 G2 Series Rack Options Installation Guide available at the following URL: http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual/c01493702/c01493702.pdf

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Each hold down bracket has three anchor holes spaced as shown in Figure 3. All six anchor positions should be used. The static vertical and horizontal loads are assumed to be carried equally by the six anchors. The front-to-rear resultant bending moment is carried by each set of three anchors separated by the distance of 38.86 inches. The side-to-side resultant bending moment is carried by the outer anchors separated by 18.19 inches at the front and 18.50 inches at the rear.

Figure 3.Bottom view of HP Tie-Down Option Kit anchor positions

Callout Distance

A 18.19 in (462.0 mm)

B 9.09 in (231.0 mm)

C 38.86 in (987.1 mm)

D 9.25 in (235.0mm)

E 18.50 in (470.0 mm)

NOTE The HP Tie-Down Option Kit contains all the hardware necessary for installation on an HP 10000 series G2 rack. Securing the rack to the floor requires additional anchoring hardware that is not provided in the HP Tie-Down Option kit.

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Anchoring methods This document identifies just a few possible anchoring methods. Each specific installation should be analyzed for the best anchoring solution. The anchoring methods described in this document can be applied to a full-depth reinforced concrete slab, a concrete fill over metal deck, or a raised computer floor. Site-specific analysis is required to identify the adequacy of the structural support system for all installations.

NOTE The methods described herein require the use of anchor bolts or studs designed to transmit structural loads by means of tension, shear, or a combination of tension and shear between the connected elements. The design strength of the anchors should equal or exceed the largest required strength due to seismic demand. The installation processes recommended by the anchor manufacturer must be followed. Manufacturers of anchor hardware are listed in the For more information section of this document.

Anchoring in solid concrete (ground floor) For ground floor applications or where the concrete slab is sufficiently thick to allow for the full embedment depth of the anchor, the method shown in Figure 4 can be used. Important parameters for the concrete are the slab thickness and the compressive strength. This example assumes the use of cracked concrete with a compressive strength of 2500 psi with no edge reinforcement. The concrete pad must be sufficiently thick to allow for the minimum embedment depth of the anchors, with sufficient remaining cover. In addition, the distance to the edge of the concrete slab and between anchors must comply with those identified for the anchors under the specified loads. The anchor plate must meet the minimum thickness and distance to the edge to allow for the load to be transmitted effectively from the rack structure to the concrete.

Figure 4. Anchoring in solid concrete (ground floor)

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Anchoring in concrete fill over a metal deck (upper floor) A typical construction technique for upper floors is to use concrete fill over a metal deck (Figure 5). The anchors in this type of floor structure must satisfy the same requirements as those given for the full-depth concrete (ground floor) slab. Through thickness anchors can also be used in this configuration with backing plates used. Site specific analysis is required to identify the adequacy of the structural support system and any anchor details.

Figure 5. Anchoring in concrete fill over metal deck (upper floor)

Anchoring in a raised floor system A rack equipped with a Tie-Down kit may also be anchored on a raised floor system. Two designs for raised floor systems are shown in Figure 6. The vertical members support the weight of equipment installed on the floors and the diagonal braces resist lateral loads cause by the seismic event. The diagonal braces can be attached either to the raised floor structure (Figure 6A) or to the supporting structure (Figure 6B). In each case, the pads for the vertical supports and diagonals must also be anchored to the slab. The adequacy of the anchors must also be predetermined. For all raised floor systems the structure must be qualified for the seismic loads at the specific site. The anchors should be secured directly to the raised floor structure where it is in contact with the supported rack. If the anchors are extended to the supporting slab structure, an analysis should be performed to ensure that the extensions are not soft springs that cannot transmit the loads. Typical anchors are designed to transmit structural loads through a combination of tension and shear between the connected elements over short lengths.

Figure 6. Anchoring methods for a raised floor system

A: Braced flooring

B: Braced support structure

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Seismic hazard locations The United States can be divided into eight basic seismic hazard regions: Alaska, Hawaii, Northwest (NW), North Central (NC), Northeast (NE), Southwest (SW), South Central (SC), and Southeast (SE) as shown in Figure 2. In addition, three specific areas are identified for seismic activity: California, New Madrid, and Charleston. The characteristics of soil at a specific geographic location is determined using the site coefficients for the full range of Site Classes A to E. Figure 7 shows the 0.2-second spectral response accelerations (SA) for each of these regions and areas for Site Class B.

Figure 7. Seismic hazard regions and areas of the continental United States

New Madrid

Charleston

NW

SC

NE NC

SW

SE

California

Data sources: United States Geological Survey (USGS) of 2003 ASCE/SEI 7-05 Minimum Design Loads for Buildings and Other Structures, 2005

Soil characteristics affect a location’s response spectrum, which is a plot of the peak and steady state response of ground motions (oscillations) at various frequencies and accelerations. Response spectra are used to analyze the reaction of structures and equipment to earthquakes.

For most cases, designs based on peak acceleration are controlled by Site Class D. Examples of the calculated response spectra for a specific geographic location and the various site classes are given in Figure 8. Because the soil structure can potentially modify both amplitude and frequency of the bedrock spectra, there are variations within this set of spectra.

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Figure 8. Design response spectra (5 %) for New Madrid: Ss = 3.40, S1 = 1.37

For this analysis a very conservative approach was taken to develop an envelope spectra for the specific site and location. By taking the maximum of all the curves at any given frequency, the overall bounding curve was developed. This is a very conservative approach because no site will have all of the worst case characteristics of the entire geographic location. The result was a design spectrum for each region. Figure 9 shows the region-specific design response spectrum for a non-structural component and is used in this analysis. The maximum credible earthquake (MCE) is identified as 1.5 times the design earthquake.

Figure 9. Enveloping design response spectra based on region

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The approach used in the reference document “ASCE/SEI 7-05, Minimum Design Loads for Buildings and Other Structures, American Society of Civil Engineers, 2005” is to identify an equivalent static force representative of the seismic load case. Table 1 shows the short period spectral acceleration, SDS, which corresponds to the maximum level on each of the spectra given in Figure 9, and the 1-second spectral acceleration (SD1). In addition, the maximum considered earthquake data extracted from ASCE/SEI 7 is also given as SS and S1. Within Table 1, the highest values are highlighted in red, the next highest in yellow, and the third highest in green

Table 1. Summary of short period and 1-second spectral accelerations

Response Acceleration (g) at 5 % damping

MCE Site Class D Site Class E

Location SS S1 SDS SD1 SDS SD1

NE 0.60 0.11 0.52 0.17 0.59 0.26

SE 0.60 0.15 0.52 0.22 0.59 0.34

Charleston 2.58 0.72 1.72 0.73 1.55 1.17

New Madrid 3.40 1.37 2.27 1.30 2.04 2.08

NC 0.60 0.20 0.52 0.27 0.59 0.43

SC 0.52 0.16 0.48 0.23 0.58 0.35

NW (1) 1.88 0.80 0.25 0.80 1.13 1.28

NW (2) 2.70 1.05 1.80 1.05 1.62 1.68

SW 1.75 0.60 1.17 0.60 1.05 0.96

California (1) 2.89 1.24 1.93 1.24 1.73 1.98

California (2) 2.75 1.18 1.83 1.18 1.65 1.89

Alaska (1) 2.18 1.68 1.45 1.68 1.31 2.69

Alaska (2) 2.28 1.80 1.52 0.80 1.37 1.28

Hawaii 2.67 1.23 1.78 1.23 1.60 1.97

As can be seen from both Figure 9 and Table 1, Alaska, the western U.S., Charleston, and New Madrid areas have significantly high accelerations. The rest of the eastern and central US regions will have significantly lower demands (typically 0.52 to 0.59 g) for anchoring hardware. For the remainder of the country the maximum design value is 2.27 g. This is an increase in demand on the equipment of 3.8 times. The requirements placed on the anchor system can be tailored to a specific location.

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Anchor design requirements Anchor design is based on an equivalent static analysis for the dynamic loading produced by the seismic event. The process is to take the seismic load and calculate the equivalent seismic design force. The analysis is associated with the anchors in concrete and the bracket fasteners. The analysis does not include or consider the structural integrity of the rack or brackets.

As identified by ASCE/SEI 7, the seismic coefficients for communication equipment, computers, instrumentation, and controls are as follows: amplification factor (ap)= 1.0 and component response modification factor (Rp)= 2.5.

The seismic design force, FP, is calculated in accordance with the following equation:

Where:

FP = seismic design force SDS = spectral acceleration, short period, as determined from Section 11.4.4 of ASCE/SEI 7 aP = component amplification factor from Table 13.6-1 of ASCE/SEI 7 IP = component importance factor WP = component operating weight RP = component response modification factors from Table 13.6-1 of ASCE/SEI 7 z = height in structure of point of attachment of component with respect to the base h = average roof height of structure with respect to base

FP need not be greater than: FP < 1.6 SDS IP WP

FP need not be less than: FP > 0.3 SDS IP WP

The horizontal seismic design force, vertical force, and resultant moment due to the horizontal seismic design force are based on component-specific factors and the seismic loads.

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Figure 10 shows the horizontal (H1, H2) and vertical (V) seismic forces acting at the center of gravity (cg) of the resulting forces (S1, S1, V) and moments (M1, M2) at the base of the rack. These forces are transmitted to the support structure through the hold-down brackets and anchors.

Figure 10. Base forces and moments resulting from horizontal and vertical seismic loads (42U HP 10000 G2 series model 10642 rack shown)

The base moments and forces indicated in Figure 10 are resolved into the axial and shear loads at the anchor locations shown in Figure 11.

Figure 11. Resulting axial and shear loads on anchors

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M8 fasteners and anchors are designed according to the calculated base forces and moments, and on the estimated axial and shear loads. The horizontal seismic forces (H1 and H2) are based on the controlling equation for FP as given previously. The vertical seismic force (V) is calculated using the formula V = 0.2 * SDS * WP. The moments at the base are the horizontal seismic force times half the height of the rack (that is, the distance between the base and the cg location). Since the cg is assumed to be in the center of the rack (approximately in the same position as H1 and H2 in Figure 10) there is no torsion.

Tables 2 through 4 include a summary of calculations for mounting an HP 10642 standard 42U rack at ground level and at rooftop level throughout the continental United States. Appendix A provides the detailed calculation data from which these results were obtained.

Table 2. Seismic forces and moments for the HP 10642 rack (see note)

Horizontal seismic design force, FP (lbs)

Vertical seismic force, V (lbs)

Seismic moment due to FP (lbs)

Location Ground

floor Roof top

Ground floor

Roof top

Ground floor

Roof top

Entire US, site class D 1532 2452 1022 1022 60,440 96,703

Entire US, site class E 1377 2203 918 918 54,316 86,905

California, site class D 1303 2084 869 869 51,387 82,219

California, site class E 1168 1868 779 779 46,062 73,699

Eastern and central US, site class D 351 562 234 234 13,845 22,152

Eastern and central US, site class E 398 637 266 266 15,709 25,134

NOTE: Physical properties of HP 10642 rack used for these calculations are as follows: Width: 23.52 inches (597 mm) Depth: 40.2 inches (1021 mm) Height: 78.9 inches (2004 mm)

Dead weight: 250 lbs (113.4 kg) Live weight: 2000 lbs (907 kg) Total weight: 2250 lbs (1021 kg)

Table 3 summarizes the maximum load calculated on any anchor based on the overall geometry of the HP 10642 rack and the locations of the six concrete anchors, the maximum load calculated on any anchor is summarized in Table 3. The shear load on the concrete anchors was based on the vector sum of the horizontal components (S1 and S2) of the seismic design force, taken to be FP in two orthogonal directions. The axial loads in the concrete anchors derive from the vertical load (V) combined with couples due to two moments (M1 and M2).

Table 3. Maximum load on concrete anchors

Shear (lb) Axial (lb)

Location Ground

floor Roof top

Ground floor

Roof top

Entire US, site class D 361 578 1842 2940

Entire US, site class E 325 519 1656 2642

California, site class D 307 491 1566 2500

California, site class E 275 440 1404 2241

Eastern and central US, site class D 83 132 422 673

Eastern and central US, site class E 94 150 479 764

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Table 4 summarizes the calculations made for the M8 bolts that attach the front and rear hold down brackets to the rack. Note that due to the wide placement of the attaching bolts, the front hold down bracket will take full side-to-side bending. The rear hold down bracket will not constrain any side-to-side moment due to the center placement of the attaching bolts. In all cases, the demand is less than the allowable demand for either the Class 8.8 or 10.9 M8 bolts.

Table 4. Maximum load on M8 attachment bolts for hold down brackets

Front hold down bracket Rear hold down bracket

Shear (lb) Axial (lb) Shear (lb) Axial (lb)

Location Ground

floor Roof top

Ground floor

Roof top

Ground floor

Roof top

Ground floor

Roof top

Entire US, site class D 1880 3004 192 306 476 744 192 306

Entire US, site class E 1690 2700 172 275 427 669 172 275

California, site class D

1559 2554 163 261 404 633 163 261

California, site class E 1443 2290 146 234 363 567 146 234

Eastern and central US, site class D

431 688 44 70 109 170 44 70

Eastern and central US, site class E

489 781 50 80 124 193 50 80

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Appendix A: Seismic load calculations for HP 10642 rack This appendix includes the seismic load calculations for the results given in Tables 2 through 4.

Table 5. Seismic load calculations for US fully loaded design basis earthquake: site class D

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Table 6. Seismic load calculations for US fully loaded design basis earthquake: site class E

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Table 7. Seismic load calculations for California fully loaded design basis earthquake: site class E

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Table 8. Seismic load calculations for California fully loaded design basis earthquake: site class E

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Table 9. Seismic load calculations for NE, SE, NC, and SC fully loaded design basis earthquake: site class D

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Table 10. Seismic load calculations for NE, SE, NC, and SC fully loaded design basis earthquake: site class E

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Appendix B: HP 10000 G2 series physical properties The seismic anchor design of the HP Tie-Down Kit is based on the physical properties of the 10000 G2 series 10642 (standard depth) 42U rack and the International Building Code (IBC) requirements for generic seismic hazards. HP 10000 G2 Series Racks are available in the sizes listed in Table 11.

Table 11. Dimensions for HP 10000 G2 series racks

HP rack type U height Width Depth Gross

Dynamic load Static load

10622 G2 22 600 mm (23.8 in)

1000 mm (39.4 in)

544 kg (1200 lb)

544.3 kg (1200 lb)

10636 G2 36 600 mm (23.8 in)

1000 mm (39.4 in)

689.5 kg (1520 lb)

907.2 kg (2000lb)

10642 G2

Standard 42 600 mm (23.8 in)

1000 mm (39.4 in)

907.2 kg (2000 lb)

1360.8 kg (3000 lb)

Extended depth

42 600 mm (23.8 in)

1200 mm (47.2 in)

907.2 kg (2000 lb)

1360.8 kg (3000 lb)

10647 G2:

Standard 47 600 mm (23.8 in)

1000 mm (39.4 in)

907.2 kg (2000 lb)

1360.8 kg (3000 lb)

Extended depth

47 600 mm (23.8 in)

1200 mm (47.2 in)

907.2 kg (2000 lb)

1360.8 kg (3000 lb)

The inertia data provided in this document are based on the HP 10000 G2 model 10642 Standard (42U) rack. The dead (empty) weight of the type 10642 rack is 250 lb. The live load is assumed to be 2000 lb, resulting in a fully-loaded (gross) weight of 2250 lb. Vertical weight is assumed to be evenly distributed, resulting in a center of gravity at mid-height.

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Appendix C: Tie-Down kit development information Development of the HP Tie-Down Option Kit was based on International Building Code requirements, generic seismic hazards, and consideration of the following factors:

• Identification of nonstructural component geometry – HP 10642 rack geometry and weight distribution – Anchor system geometry – Occupancy category – Importance factor – Seismic design category

• Identification of seismic hazards – Seismic ground motion values – Site classes – Site response coefficients – Design ground motion coefficients – Spectral response accelerations and design response spectrum

• Seismic anchor load analysis – Equivalent force method

The following documents were referenced during the development of the Tie-Down kit:

• International Building Code (IBC), International Code Council, Inc., 2006 • ASCE/SEI 7-05, Minimum Design Loads for Buildings and Other Structures, American Society of

Civil Engineers, 2005 • ICC-ES-AC156, Acceptance Criteria for Seismic Qualification by Shake-Table Testing of

Nonstructural Components and Systems, ICC Evaluation Service, Inc. 2007 • GR-63-CORE, NEBSTM Requirements: Physical Protection, Issue 3, Telcordia Technologies, 2006. • IEEE-344, Recommended Practice for Seismic Qualification of Class 1E Equipment for Nuclear

Power Generating Stations, The Institute of Electrical and Electronics Engineers, Inc., 2004 • FEMA 450, NEHRP Recommended Provisions and Commentary for Seismic Regulations for New

Buildings and Other Structures, Federal Emergency Management Association 2003

For more information For additional information, refer to the resources listed below.

Resource description Web address

HP Tie-Down Option Kit Installation Instructions

http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00598467/c00598467.pdf?jumpid=reg_R1002_USEN

HP 10000 G2 Series Rack Options Installation Guide

http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual/c01493702/c01493702.pdf

Anchor manufacturers (see note): Red Head® Hilti® Co.

http://www.itwredhead.com

http://www.hilti.us

NOTE: Mention of manufacturers herein should not be interpreted as an endorsement or recommendation of those manufacturers’ products by HP.

Call to action Send comments about this paper to TechCom@HP.com.

© 2004, 2009 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice. The only warranties for HP products and services are set forth in the express warranty statements accompanying such products and services. Nothing herein should be construed as constituting an additional warranty. HP shall not be liable for technical or editorial errors or omissions contained herein. ITW Red Head is a registered trademark of Illinois Tool Works, Inc. Hilti is a registered trademark of Hilti AG, Schaan.

TC091004BP, October 2009