EN 1991-1-6 2005 Overview: Construction Stage Loads and Site Execution Scenarios (Eurocode 1 Series)

The Unseen Phase: Why Temporary Loads Demand a Permanent Standard

Imagine a project manager overseeing the construction of a landmark cable-stayed bridge. The final design, compliant with all permanent load standards, is a masterpiece of engineering. Yet, the most critical phase—the months when the bridge exists only as incomplete piers, temporary falsework, and cranes operating at their limits—is governed by a different, often overlooked, set of rules. This is the domain of EN 1991-1-6. For engineers and site managers, this standard isn’t about the finished structure; it’s about the hazardous journey of getting there. It provides the definitive framework for defining actions on structures during execution, transforming the chaotic, transient world of a construction site into a series of quantifiable, manageable engineering scenarios.

What is EN 1991-1-6? The Rulebook for the Build

EN 1991-1-6, formally titled “Actions on structures – Part 1-6: General actions – Actions during execution,” is a core part of the Eurocode 1 suite. In practical terms, it is the essential reference for any professional responsible for the safety and stability of a structure from groundbreaking to handover. While other Eurocodes define what a structure must withstand in its lifelong service, this standard answers the critical question: What loads must it withstand while it is being built?

A consulting engineer uses it to specify the design loads for temporary works like scaffolding and formwork. A construction director references it to plan the sequencing of heavy lifts, ensuring the partially built structure can handle the imposed stresses. It bridges the gap between the design office’s permanent calculations and the site team’s dynamic reality, ensuring that safety is engineered into every phase of construction, not just the final product.

Core Application Scenarios: From Planning to Pouring

The standard’s value becomes crystal clear in specific, high-risk construction scenarios:

* Heavy Lifting and Installation: Planning the placement of a 100-tonne precast segment on a viaduct or a major pressure vessel in a chemical plant. EN 1991-1-6 provides methodologies to account for dynamic amplification, impact, and out-of-service wind loads on both the element being lifted and the supporting structure.
* Sequential Construction Analysis: Building a multi-story concrete frame or a long-span steel roof. The standard guides engineers in analyzing the structure at each critical stage—when only the first few floors exist, when the cantilever is unsupported, or before the final connections are made—ensuring stability throughout the process.
* Temporary Works Design: Designing falsework for a bridge deck pour or shoring for an underground excavation. It classifies the nature and magnitude of loads from stored materials, personnel, equipment, and environmental actions specific to the construction period.
* Specialized Construction Methods: Implementing incremental launching for a bridge, slip-forming for a chimney, or tunnel boring machine operations. These methods introduce unique, transient load cases that are explicitly considered within the standard’s framework.

Decoding Key Requirements Through Scenario Stories

The technical heart of EN 1991-1-6 is best understood not through clauses, but through on-site stories.

Scenario: The Tower Crane Conundrum
A contractor is erecting a high-rise in a coastal city. The permanent structure is designed for the region’s ultimate wind speeds. However, the tower crane, fixed to the rising core, presents a different challenge. EN 1991-1-6 guides the team to consider the crane’s exposed surface area and the appropriate wind load for the construction period, which may differ from the permanent design wind load. It also mandates considering the dynamic effects if the crane is to be “jumped” to a higher level. Failure to apply these specific construction-phase loads could lead to catastrophic instability during a storm.

Scenario: The Precast Puzzle
A team is assembling a large precast concrete stadium roof. Each massive beam must be held in a temporary position before final post-tensioning. The standard requires the team to define “accidental actions” for this temporary state, such as the unintended impact from an adjacent element during placement or the failure of a temporary prop. This leads to a robust temporary bracing design that safeguards against these execution-phase risks, which are not covered under the final, continuous-structure design codes.

A Unique Scenario-Specific Requirement: The Classification of Execution Phases
One of EN 1991-1-6’s most powerful tools is its formal classification of construction stages (e.g., storage, assembly, stabilization). For each class, it defines representative values for variable actions (like imposed loads from workers and equipment) and combination factors. This allows for a rational, less conservative approach than simply using final building loads, optimizing temporary works design while maintaining safety. For a project manager, this means being able to justify that the load from a stack of bricks on a completed floor slab during fit-out is fundamentally different from the load during the structural concrete pour.

Regulatory Context and Cross-Border Coordination

As a European Norm (EN), EN 1991-1-6 is published by the European Committee for Standardization (CEN). Its application is mandatory for public works in the EU and often forms the basis for private projects. Its true power in cross-border scenarios lies in its systematic approach. For a German engineering firm working with a Turkish contractor on a project in Poland, this standard provides a common, unambiguous language for defining construction loads. It resolves conflicts that might arise from differing national traditions for temporary works design.

When compared to more generic guidelines often found in regional codes, EN 1991-1-6’s structured, principle-based methodology offers greater consistency and traceability. It doesn’t just suggest good practice; it provides an engineered framework for verification.

Who Relies on It and the Risks of Ignoring It

* Temporary Works Designers: They use it as the primary load basis for their calculations.
* Construction Planners and Method Engineers: They reference it to develop safe sequence-of-work documents.
* Project Managers and Site Supervisors: They rely on the plans and designs derived from it to manage on-site safety.
* Principal Designers (under CDM regulations): They use it to ensure construction phase risks are adequately mitigated in the design.

The risks of non-compliance or misapplication are severe and direct:
* Catastrophic Collapse: The most obvious risk is structural failure during construction, leading to loss of life, as seen in historical falsework and crane collapse incidents.
* Costly Delays and Rework: Discovering that temporary supports are inadequate mid-pour can halt a project for weeks and incur massive remedial costs.
* Legal and Contractual Disputes: In the event of an incident, the absence of compliance with this recognized standard can be a central point of liability.
* Reputational Damage: A high-profile construction failure erodes client trust and regulatory confidence.

A Real-World Scenario: The Bridge Deck Launch

A European contractor was awarded a contract to build a river bridge in Southeast Asia. The design called for incremental launching of the steel box girder deck. The local code had limited guidance for the complex, changing load cases during launch—torsion from uneven friction, point loads from launching noses, and combined wind effects on the long, slender, unsupported deck.

The project team applied EN 1991-1-6 to systematically define each execution stage: storage of segments, assembly on the launch pad, each incremental launch step, and the final lowering onto bearings. For each stage, they determined characteristic loads for equipment, personnel, and environmental actions. This disciplined approach allowed them to:
1. Design a robust launching nose and temporary piers.
2. Establish clear wind speed limits for each operation phase.
3. Provide the client and local authorities with a verifiable, internationally recognized safety plan.

This use of the standard prevented potential instability during launch and satisfied the due diligence requirements of international insurers, smoothing the path to project completion.

Common Misconceptions to Avoid

1. “The permanent design code covers it.” A dangerous assumption. Permanent codes like EN 1992 (concrete) or EN 1993 (steel) define resistance and often reference execution, but the definition of the loads themselves during construction is the exclusive domain of EN 1991-1-6.
2. “It’s only for the temporary works designer.” While vital for them, its principles are crucial for the entire project team. The construction method, chosen by the planner, directly dictates the loads that must be considered. Early collaboration between permanent and temporary works designers, guided by this standard, is key to buildability and safety.

In essence, EN 1991-1-6 is the indispensable script for the most dangerous act in a structure’s life: its own birth. By translating the uncertainties of the construction site into defined engineering parameters, it empowers professionals to build not just with ambition, but with calculated, stage-by-stage certainty.