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HDU Heavy Duty Holdown

Model: HDU8-SDS2.5

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Please note: The HDU Holdown is being discontinued and replaced with the new HDUE™ Holdown. Please get in touch with our engineer via the Contact page. 

Simpson Strong‑Tie offers a wide variety of holdown devices engineered and tested to perform and manufactured to the highest quality standards. The HDU Holdown is pre‑deflected during the manufacturing process, virtually eliminating deflection under load due to material stretch. This super heavy duty HDU is suitable for residential and commercial projects, sub diaphragm floor, seismic upgrades, mid floor vertical connection applications. 

 

The HDU installs with Simpson Strong‑Tie® Strong‑Drive® SDS Heavy‑Duty Connector screws which install easily, reduce fastener slip and provide a greater net section when compared to bolts. The HDU is also ideal for retrofit or new construction projects. They provide high-strength, post-pour, concrete-to-steel connections.

Please check the Corrosion Information to see if it is suitable for your application.

Material
  • HDU8: Carbon Steel 3.5mm thick
  • HDU14: Carbon Steel 4.5mm thick
Finish

Z275 Galvanised

Features & Benefits
  • Pre-deflected body virtually eliminates deflection due to material stretch
  • Uses Strong-Drive® SDS Heavy-Duty Connector screws which install easily, reduce fastener slip and provide a greater net section area of the post compared to bolts
  • Strong-Drive SDS Heavy-Duty Connector screws are supplied with the holdowns to ensure proper fasteners are used (HDU8-SDS2.5 includes 20 – SDS 6.4mm x 64mm screws)
  • Easy to install
  • No stud bolts to countersink at openings
Installation
  • Use all specified fasteners 
  • The HDU requires no additional washer
  • Strong‑Drive SDS Heavy‑Duty Connector screws install best with a low speed high torque drill with a 3/8” hex head driver
 
 
Model No. Table

Model No.

Dimensions (mm)

Fasteners

Wall Framing Stud(s) (mm)

Country

Design Tension Capacity (kN)

Strap
Thickness

W

H

B

CL

Anchor Hole Dia. (mm)

Post (Nails: No. - Length x Dia., Screws: No. - Dia. x Length, mm)

HDU8-SDS2.5

3.5

75

420

90

35

23

20 – SDS6.4 x 64

(90 or 2/45)7 x 90

AU

k1 = 1.14

36.2

NZ

k1 = 1.0

29.8

HDU14-SDS2.5

4.5

79

653

93

41

26

36 – SDS6.4 x 64

(90 or 2/45)7 x 140

AU

k1 = 1.14

68.6

NZ

k1 = 1.0

56.6
  1. Design Capacity is the lesser of (1) the Characteristic Capacity multiplied by the Capacity Factor, and applicable k modification factors following AS 1720.1 and (2) the Serviceability Capacity which is the load at 6.4mm joint slip, which includes fastener slip, anchor elongation and holdown deformation. Design Capacity is the minimum of test data and structural joint calculation.
  2. The Capacity Factor (ϕ) for AU is 0.85 for nails and screws for structural joints in a Category 1 application, and for NZ is 0.8. Reduce tabulated values where other Category applications govern.
  3. Duration of Load Factor (k1) is as shown. Reduce Duration of Load Factor where applicable. Capacities may not be increased.
  4. Timber species for joint design is seasoned Radiata Pine, which is Australia Joint Group JD4 per AS 1720.1 Table H2.4.
  5. The Designer must specify anchor bolt type, length and embedment.
  6. Anchor bolt nut should be finger tight plus 1/3 to 1/2 turn with a hand wrench. Care should be taken not to over‑tighten the nut.
  7. Minimum 90mm or 2/ 45mm thick post or studs required. Number of total studs or post size to meet axial load demand, to be determined by designer. Multiple studs connected independently of holdown fasteners.
  8. Structural composite timber columns have sides that either show the wide face or the edges of the timber strands/veneers known as the narrow face – values in the table reflect installation into the wide face.
  9. Holdowns and tension ties may be installed raised up to 460mm above the top of the concrete with no load reduction, provided that additional elongation of the anchor rod is taken into account.

Model No.

H
(mm)

Fasteners

Stud
Quantity

Stud
Member Thickness (mm)

LRFD Tension Load

(kN)

Deflection at LRFD Load4 (mm)

Nominal Tension Load5 (kN)

Anchor Hole Diameter (mm)

Stud Fasteners

S/HDU9

327

22

18 - 14g

2

0.75

49.5

4.8

58.6

2

0.95

68.9

6.4

97.0

2

1.15

71.0

5.7

108.9

Steel Fixture

4.76

91.2

4.5

139.9
  1. Designer shall specify the foundation anchor material type, length, embedment and configuration.
  2. Stud design by Specifier. Tabulated loads are based on a minimum stud thickness for fastener connection.
  3. Self-drilling tapping screws of 6.35 mm diameter can be substituted for 14g.
  4. Deflection at LRFD Loads includes fastener slip, holdown elongation and anchor bolt elongation (L=102mm).
  5. Nominal Tension Load is based on the average ultimate (peak) load from tests. AISI Lateral Design standard requires holdowns to have nominal strength to resist the lesser of the amplified seismic load or the maximum force the system can deliver.

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