Permit Details
Permit Number: Z-21.8-2137
Applicant: Hilti Deutschland AG, Hiltistraße 2, 86916 Kaufering, Germany
Validity: From 27 March 2025 to 21 December 2026
Subject of Decision: Hilti concrete screw HUS4 for temporary fastening in concrete
This document grants a general construction technique permit (allgemeine Bauartgenehmigung). It replaces the previous permit dated 21 December 2021 and confirms the approval granted for the first time on 21 December 2021.
General Provisions
The general construction technique permit confirms the fitness for application of the subject concerned within the meaning of the Building Codes of the federal states (Landesbauordnungen). This decision does not replace other legally required permits, approvals, or certificates for construction projects. It is granted without prejudice to third-party rights. Copies of this decision must be made available to installers and at the place of application. Partial publication requires DIBt consent. Texts and drawings in promotional material must not contradict this decision; the German version prevails in case of discrepancies. The decision may be revoked or amended based on new technical findings. It is based on the applicant's submitted information and documents.
Special Provisions
Subject Concerned and Field of Application
The subject is the Hilti concrete screw HUS4, available in sizes 8, 10, 12, 14, and 16 mm, as per European Technical Assessment ETA-20/0867. It is a special screw with a hexagon head or thread connection, made of galvanized steel. Anchoring involves screwing into a pre-drilled cylindrical hole, where the special thread cuts into the base material, creating mechanical interlock. The installed anchor is illustrated in Annex 1.
The HUS4 screw is approved for anchoring in reinforced and unreinforced normal weight concrete with strength classes C20/25 to C50/60. It can be fastened and loaded before the concrete reaches its characteristic strength, subject to verification per Section 2.3.1. It is intended for temporary fastening of construction site equipment like shoring props, fall protection, or scaffolds. The screw can be reused in other drill holes after unscrewing, but a drilled hole cannot be reused after fastener removal. Reusability requires visual inspection and checking with a sleeve setting jig (Section 2.3.3). Installed fasteners must be checked for damage (e.g., corrosion) and replaced if necessary. The screw is suitable for use in both cracked and uncracked concrete and for temporary use in internal and external conditions.
Provisions for Planning, Design, and Execution
Planning
Anchorages must be planned using good engineering practice, with verifiable calculations and design drawings that account for the loads. Design drawings should specify exact positions and sizes. Minimum spacing (edge and center-to-center) and minimum member thicknesses, as detailed in Annexes 6, 7, and 8, must be observed.
Design
These provisions cover the verification of immediate local force transmission into the concrete. The transfer of anchored loads within the member must be verified separately. Additional stresses due to constraint (e.g., temperature fluctuations) in the screw, fixture, or member must be considered.
Verifications with Resistances for All Load Directions
For combinations 1 and 2 (edge distance c₁ and member thickness hmin per Annexes 6, 7, 8, Tables 5, 6, 7), the design action FEd must not exceed the design resistance FRd. Design resistances apply to all load directions and failure modes, as listed in Annex 11, Table 8, based on screw size, embedment depth, and concrete strength.
Verifications with Separate Resistances for Axial Tension and Shear
For combination 3 (edge distance c₁ and member thickness hmin per Annexes 6, 7, 8, Tables 5, 6, 7), design actions NEd and VEd must not exceed design resistances NRd and VRd. For combined tension and shear loads, specific interaction conditions apply (see Section 2.2.3).
Execution
General
Installation must follow design drawings (Section 2.1) and setting instructions (Annexes 9, 10). The screw can be used in young concrete if its strength reaches at least 8 MPa. The installer must provide a declaration of conformity.
Drilling of Hole and Cleaning
Drill holes must be positioned considering reinforcement to avoid damage. Holes must be drilled perpendicular to the concrete surface using carbide masonry drill bits meeting DIBt specifications. Drill bit characteristic values must be verified. Drill bit diameter, cutting diameter, and hole depth must match Annexes 6, 7, 8, Tables 5, 6, 7. Drilling dust must be removed from wall/floor positions. Cleaning is not required for upward drilling or for downward/horizontal drilling followed by three ventilation cycles (Annex 9). If a hole is drilled incorrectly, a new hole must be drilled at a distance of at least twice the depth of the incorrect hole.
Installation of Screw
The screw is intended for single-hole temporary use. It can be reused in other holes but not in the same hole twice. Before reuse, thread wear must be checked with a sleeve setting jig (HRG). Reuse is permitted only if the screw does not protrude from the sleeve. Damaged screws (e.g., due to corrosion) must not be reused. Installation can be done with a torque impact screw driver, preferably with an automatic cut-off device. Correct installation is confirmed if the base plate is flush against the concrete, the fastener head/washer rests on the base plate, the fastener cannot be easily turned further, and the correct embedment depth (hnom) is achieved.
Inspection of Execution
A contractor or competent representative must be present during installation to ensure proper execution. Records of concrete strength verification (Section 2.3.1) and proper installation must be kept. Installed fasteners require regular checks by the site manager or representative as per Section 1.2. Records must be available on-site during construction and provided to inspectors upon request, and retained for at least 5 years after project completion.
Annexes
Annex 1: Installed Condition
Illustrates the HUS4-H (hexagon head) and HUS4-A (external thread) screws installed in concrete. Key dimensions shown include clearance hole diameter (df), fixture thickness (tfix), nominal embedment depth (hnom), drill hole depth (h1), and minimum member thickness (hmin).
Annex 2: Screw Types and Material
Table 1: Screw Types lists Hilti HUS4-H (sizes 8, 10, 12, 14, 16), HUS4T-H (sizes 8, 10), and HUS4-A (sizes 10 with M12, 14 with M16), all galvanized with hexagon head or external thread configurations.
Table 2: Material specifies the HUS4 concrete screw (all types) is made of Carbon steel with an elongation at break A5 ≤ 8%.
Annex 3: Dimensions and Head Marking HUS4-H and HUS4T-H
Table 3 provides dimensions (nominal diameter, thread pitch, nominal embedment depth, screw length) and head markings for HUS4-H and HUS4T-H screw types.
Annex 4: Dimensions and Marking HUS4-A
Table 4 details dimensions (nominal diameter, metric thread connection, thread pitch, embedment depth, screw length) and marking for HUS4-A screw types, including length identification codes.
Annex 5: Installation Parameters
Illustrates installation parameters (c1, c2, s, SW, SW1, SW2, h1, hnom, hmin, tfix) for HUS4(T)-H and HUS4-A screws, referencing Tables 5 to 7 for specific values.
Annex 6: Installation Parameters HUS4-8 and 10
Table 5 provides detailed installation parameters for HUS4 screws in sizes 8 and 10, covering embedment depths, drill hole diameters, clearance holes, wrench sizes, installation torque, drill hole depths, and spacing/edge distance requirements for three combinations.
Annex 7: Installation Parameters HUS4-12 and 14
Table 6 provides detailed installation parameters for HUS4 screws in sizes 12 and 14, covering embedment depths, drill hole diameters, clearance holes, wrench sizes, installation torque, drill hole depths, and spacing/edge distance requirements for three combinations.
Annex 8: Installation Parameters HUS4 16
Table 7 provides detailed installation parameters for HUS4 screws in size 16, covering embedment depths, drill hole diameters, clearance holes, wrench sizes, installation torque, drill hole depths, and spacing/edge distance requirements for three combinations.
Annex 9: Installation Instructions (Drilling and Cleaning)
Details the process of hammer drilling for Hilti HUS4 screws, emphasizing temporary use and reuse guidelines. It covers marking drilling depth, creating the hole, cleaning procedures (when required or not), and handling incorrect drillings. It notes that screws showing visible damage or protruding from the sleeve must not be reused.
Annex 10: Installation Instructions (Setting and Checking)
Describes the process of setting the concrete screw according to installation parameters and screw length selection to maintain the nominal embedment depth. It outlines the setting check criteria: fixture flush against concrete, fastener head/washer resting on base plate, fastener not easily turnable, and correct embedment depth achieved.
Annex 11: Design Resistances
Table 8 presents design resistances for all load directions for cracked and uncracked concrete (Combinations 1 and 2), based on concrete compressive strength and embedment depth.
Table 9 presents design resistances for axial tension and shear for cracked and uncracked concrete (Combination 3), based on concrete compressive strength and embedment depth. It also includes interaction conditions for combined tension and shear loads.
Technical Data and Specifications
The Hilti HUS4 concrete screw is designed for temporary fastening in concrete. It is available in various sizes and configurations (hexagon head, external thread) and is made of galvanized carbon steel.
Key technical specifications include:
- Material: Carbon steel (elongation at break A5 ≤ 8%)
- Concrete Strength: Suitable for C20/25 to C50/60 concrete.
- Installation Torque: Specific maximum values apply for certain types (e.g., 20 Nm for A-type, 80 Nm for some 12/14mm types).
- Embedment Depths: Vary by screw size and configuration, ranging from 50 mm to 130 mm.
- Drill Hole Diameters: Range from 8 mm to 16 mm.
- Design Resistances: Detailed tables (Annex 11) provide load-bearing capacities (FRd, NRd, VRd) based on concrete strength and embedment depth.
The document provides comprehensive tables for installation parameters, including edge distances, member thicknesses, and drill hole depths, crucial for correct and safe application.
Installation Guidelines
Proper installation involves precise drilling, cleaning (where necessary), and setting of the screw. The Hilti HUS4 is intended for temporary use, and guidelines for reuse and inspection are provided. Adherence to specified dimensions, torque values, and embedment depths is critical for performance and safety.
