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Glass Structures & Engineering

, Volume 4, Issue 1, pp 17–27 | Cite as

Revolving entrance doors: Machines or structural elements?

  • Andreas HaeseEmail author
Case Study

Abstract

Revolving entrance doors—usually built as some kind of all glass structure—are part of many publicly accessible buildings. As the architectural demands rise regarding transparency and slenderness of façade members, the entrance doors have to and do go along with these demands. But even if the façade is designed carefully and verified according all relevant standards, the revolving doors are usually considered as a machine, coming with some certificate. This point of view is mostly shared by the manufacturer and the basis for the call for proposals. The certificates provided by the door manufacturer considers the electrical safety, the safety aspects for people handling and using the doors regarding the risk of persons being jammed or hit by the turning door leaves, but not the structural safety of the door system in means of resistance to live, dead, wind or earthquake loads. If we look at the design and verification effort made for standard façade elements, even windows on the one hand, and the different failure consequences for windows and revolving doors on the other hand, it becomes obvious that especially to non-standard and large-scale doors should be paid some attention regarding its structural safety. Below the legal situation of revolving doors is considered in the European context and two quite different examples of revolving doors are discussed regarding their structural assessment.

Keywords

Revolving doors Structural safety Glass as structural element 

1 Introduction

This paper considers the safety of revolving entrance doors regarding its structural capacity and structural safety. Details about the regulatory situation will be given in the following chapters, but the main conclusion from recent experience is, that for most installed revolving doors no structural verification is made. The following figure tries to illustrate the mismatch regarding usually applied structural safety requirements by comparing the requirements for a—standard—window and a revolving door (Fig. 1).
Fig. 1

Comparison of usually applied structural safety requirements for a windows and b revolving doors (with kind permission of Blasi GmbH)

Nevertheless, vigilant builder-owners and/or their façade consultants are aware of this and demand structural verification for the doors to be installed, independent of the regulatory situation.

2 Classification of revolving doors and corresponding regulations

2.1 Classification

Typical revolving doors can be differentiated regarding their drive function. There are
  • manually operated revolving doors

  • manually operated revolving doors with auxiliary drive

  • automatic revolving doors

The auxiliary drive is used to help the person passing the door to accelerate the turnstile and is released when the turnstile reaches a certain rotational speed, but it does not operate or brake the turnstile. Automatic doors recognize approaching persons and start the turnstile, operate it during traffic and slow it down if not used.

2.2 Regulations

Automatic revolving doors were regulated in DIN 18650-1 and DIN 18650-2 in Germany and are now regulated in (DIN) EN 16005 on European level, both based on the EC machinery directive thus regarding the doors as machines. The regulation content is mostly identic and covers operational safety aspects. Regarding structural safety both standards are limited to the very general requirement that automatic doors must be built in such a way that they can withstand the stress from intended use and foreseeable misuse.

Standard or manually operated exterior doors are considered in (DIN) EN 14351-1 and in contrast to the automatic door here the resistance of the door (or window) to wind, snow or permanent loads is considered and a verification required. One might assume that these requirements automatically apply for automatic doors too, but the standard itself explicitly excludes revolving doors.

Although the exact legal status of automatic revolving doors within the technical building regulations is complicated, the requirement for a structural assessment becomes obvious by referring to the general building law. The building law is different in every country but any building law requires the owner and builder to build things safe for the intended use and for the intended duration of use. There is no reason, why the safety demands for revolving doors should be any less than for a window.

As a result, the structural assessment—if demanded—is usually required according to the standards provided by the technical building regulations as the Eurocodes, ASTM-standards or national codes (e.g. codes for verification of glass members).

3 Revolving doors as part of the building façade

3.1 Architectural integration

From the architectural view revolving doors usually form part of the building façade or of the entrance façade, mostly separated from the main façade by an offset and/or a portal frame.

Especially if the surrounding façade is a mullion and transom system, the door is required to fit into the façade grid without—visible—additional posts in order to appear as an integrated element (Fig. 2).
Fig. 2

Entrance façade with integrated revolving doors (with kind permission of Blasi GmbH)

3.2 Technical integration

In contrast to the architectural demand of integrating the door in the façade, from the structural point of view, the requirement is quite the opposite: separation from the façade to allow displacement normal to the facade. Usually two wind load scenarios have to be considered, wind normal to the façade surface and wind parallel to the façade surface (Fig. 3):
Fig. 3

Wind load scenarios

In both scenarios an all-over wind pressure inside the door is assumed, acting on the drum walls as well as on the turnstile. Half the wind load on the turnstile is transferred to the support frame at the upper turnstile support.

The common approach for doors would be to connect it to the bottom and to the structure above or besides, but the deformation behaviour is incompatible. For wind loads normal to the façade surface, the door is very stiff due to the drum walls. This is positive as the doors functionality demands small deformations in operation. The façade on the other hand is allowed a certain deflection e.g. 5 mm + L/300 for 3.000 mm < L < 7500 mm according to EN 13830 thus allowing 15 mm for a 3 m high façade post.

Therefore, if façade and door would be connected, it would not be the door being supported by the façade, but the façade being supported by the door and effectively transferring additional load from the façade to the door.

As a result, revolving doors, integrated in curtain wall facades must be designed as stand-alone structures, fixed only to the base they stand on. For this purpose, it would be very helpful, if the drum walls could be made of only two glass elements, one on each side of the door. But as the revolving door was invented to prevent the cold or heat coming in or geting out of the building, this kind of door is usually installed with the purpose of thermal insulation, integrated in an insulating façade. Therefore, the walls cannot run through the façade in one piece but must be separated along the façade section.

4 Safety aspects

For automatic doors, the regulations mentioned above demand the door control to prevent
  • persons from being hit by the turnstile

  • persons or body parts from being jammed between turnstile edge and drum wall edge

  • hands from being jammed between turnstile and inner drum wall surface

  • feet from being jammed between turnstile and floor

The above-mentioned safety requirements are usually achieved by
  • limiting the rotational speed

  • emergency stop buttons

  • active braking by the drive unit

  • hinged door leaves that give way on a certain horizontal force (break-out function)

  • extensive sensor-controlled surveillance

As explained in Sect. 2.2, the provided standards do not consider structural safety in terms of technical building requirements.

5 Structural verification

5.1 Structural system

As revolving doors usually are designed and engineered as machines, there is no obvious frame that can be considered as “the” load carrying structure. It is the combination of many members and load paths that provides the load carrying capacity and stability. However, for a proper verification by calculation, the bearing structure must be defined. Its main parts are the vertical posts, a horizontal ring element on these posts and the glass infills. The ring element connects the posts and carries the door roof. The upper support of the turnstile in the ring centre is usually connected with steel rods to the ring structure (Fig. 4).
Fig. 4

Typical door structure

Minimizing the steel structure, the stiffening provided by the glass infills becomes more important.

5.2 Structural safety concept

Up to now there are no glass design standards enforced that allow the glass to be used as a structural member for in-plane loads. So, if the glass shall be used as load carrying member, it significantly increases the effort to be made on the assessment and the approval.

Basically, there are three strategies for the verification process:
  1. (a)

    steel as (sub-)structure to be verified for ULS and SLS, glass as infill—wind loads only

     
  2. (b)

    steel for safety (ULS), steel and glass for usability (SLS)

     
  3. (c)

    (steel+) glass as load bearing at SLS and ULS

     
As explained above, even standard revolving doors are highly detailed machines with minimized elements. Therefore, the approach of designing the door using only the steel members as support frame would lead to a far less filigree design than even standard doors and would be unacceptable.
Fig. 5

First (a) and final (b) turnstile design (with kind permission of Blasi GmbH)

Approach (b) allows the stiffening effect of the glass to be taken into account for the verification of deformation behaviour but without demanding high efforts on the “bureaucratic side” as glass breakage is only as critical—regarding structural safety—as it would be in a ground floor window.

If approach (c), using glass as structural members has been chosen, there are many options to minimize the steel elements and use the glass load carrying capacity instead. Of course, this goes along with higher effort in verification to comply with the legal requirements for non-standard glass structures.

In the following chapters two examples, one for each approach (b) and (c) will be shown and explained.

5.3 Regulations

Defining the regulations, standards and codes the verification shall be based on is the first important step in the design process. Unlike the building itself that is usually built or at least assembled at its final destination with elements designed and produced for this certain building, revolving doors are usually ordered from one of very few (quality) producers that sell in all parts of the world.

The building law usually requires the builder to comply with the regulations that are valid where the building is erected. This applies not only to the design codes but down to the product specifications. This is, what makes it almost impossible to verify standard door systems ex post as it is very complicated—time consuming and expensive—to get materials and products retroactively approved.
Fig. 6

Deformations at SLS with steel frame only: max \(\hbox {w} \approx 70\,\hbox {mm}\)

The two following examples will show, what difference the installation location can make to the design process.

6 Example 1: 6 m door with steel frame

6.1 Door specifications

The challenge of the first example was the door size with an overall height of approx. 6 m and a width of approx. 4.5 m, integrated in a façade with the deformation problems as discussed above. The door was to be installed in Dubai UAE as main entrance to a hotel. It was agreed, that the verification could and should be done according European and German standards due to the lack of—consistent—local regulations.

The first design considered a turnstile with the same height as the door itself, but it turned out, that for the drive technology available, the turnstile became too heavy to fulfil the safety requirements as mentioned above. The turnstile height had to be reduced to 4.5 m resulting in a different design (Fig. 5):

6.2 Deformations

The design strategy for this door was to design a frame (without glass infills) to be verified at and optimized for ULS, allowing larger deformations, and to use the glass infills to reduce the deformation to an acceptable degree (Figs. 6, 7).

The comparison of the resulting deformations shows the reduction of deformations by the glass infills. It also demonstrates the better stiffening effect for loads normal to the façade than for loads parallel to the façade due to the drum wall orientation and the—necessary—drum wall separation at the façade intersection.

The given deformation criteria were, that under full wind load the induced turnstile inclination may not cause contact of the lower edge of the turnstile wings to the floor.
Fig. 7

Deformation at SLS—steel frame with bonded glass infills

6.3 Glass drum walls

The glass drum walls were bonded to the steel frame continuously to allow an even load transfer to activate the shear panel effect of the drum walls. Additionally, setting blocs were placed between glass edge and steel frame to prevent glass-steel contact in case of bond failure. Although the bond was not critical for the door stability and structural safety, the bond geometry was designed on the basis of the resistance values according ETAG 002, respectively the bond approval referring to the ETAG.
Fig. 8

Wind load on the turnstile wings

Fig. 9

Door installed within different surrounding façade types (with kind permission of Blasi GmbH)

Due to the curved shape and the thereby increased stiffness and resistance, the effect of the wind load is quite small for the drum walls. Governing are local effects close to the glass edge. The drum walls were produced by a German manufacturer with a general approval for monolithic and laminated curved glass. The approval (AbZ) provides resistance values for surface and edge zones, based on the allowable stress design. Thus the verification of the glass can be done with the characteristic loads (SLS for steel structure).
Fig. 10

All-glass revolving door (with kind permission of John Voorhees from MacStories.net)

6.4 Turnstile

As explained above, an all-over wind load was assumed inside the door thus acting on the turnstile wings (Fig. 8).

The door wings are linearly supported on all four sides in a steel frame. Clamping the glass along the inner vertical edge was not possible, as the necessary width for a proper clamping was not acceptable for design reasons. Thus, the wind load on the turnstile wings was mostly transferred locally where the horizontal frame profiles were connected to the turnstile axis, leading to a highly stressed connection detail.
Fig. 11

Load paths for clamped curved glass panels

6.5 Result

The door discussed above has been installed several times around the building. As part of a high-rise building, the door size only becomes apparent if persons to compare with are nearby. At some doors, the design could have been quite different as a supporting structure would have been available on both sides of the door (ref. Fig. 9b).

7 Example 2: all-glass door

7.1 Door specifications

The design of the second example was driven by the ambition to minimize steel parts to the absolute minimum and to maximize transparency in order to fit into the all-glass building façade.

Two identical doors were installed in a flagship store in Chicago (USA). They are flanked by escape doors and placed in a portal frame. Although the portal frame seems to support the roof and the turnstile axis, the door is structurally independent of the adjacent façade and the portal frame, due to incompatible deformation behaviour. The doors are operated manually with an auxiliary drive (Fig. 10).

As the doors are installed in the United States, local regulations apply regarding design codes and product specifications. The four glass drum walls support the one-piece glass roof. At the centre of the glass roof is the upper bearing of the turnstile axis. Neither glass roof nor turnstile connect to the portal frame.

7.2 Glass drum walls

The steel profiles at the vertical edges of the glass drum walls are basically protecting the glass edges. They cannot be considered as a frame, as the section width of approx. 30 mm is too small to provide relevant stiffness to the structure. Thus, the glass drum walls have to provide both, the load carrying capacity for vertical loads as well as the stiffness for horizontal loads. This was achieved by drum walls, made of three-ply laminated glass with sentry glass\(^{\circledR }\) interlayer, that were clamped to the concrete base around the clearance under the door floor.

Curved glass panels clamped along their curved edge provide two load paths to induce the bending moment:
  • pair of horizontal (line) forces (H and \(\hbox {H}'\) in Fig. 11)

  • vertical forces—distributed or local at the 3 (!) setting blocks—in opposite directions at the edge centre and near the glass edge (V and \(\hbox {V}'\) in Fig. 11).

On the safe side, two scenarios have been investigated for the clamping detail at the bottom edge of the drum walls. Transferring the fixing moment with and without considering the vertical constraint as the accurate stiffness ratio of the two load paths is difficult to determine. The resulting reactions have been determined for both scenarios in the global model.

The resulting stresses have been determined in a detail model and have been verified according ASTM E1300 for a failure probability of 0.001 assuming a load duration of 3 s (wind load).

Considering the shear effect of the interlayer, the deformations due to dead load and wind load are rather small. Again, the door deformation is smaller for wind loads normal to the façade (Fig. 12).
Fig. 12

Drum wall deformation \(\hbox {w}_\mathrm{max} \approx 4\,\hbox {mm} \ldots 8\,\hbox {mm}\)

Fig. 13

Structural bond between glass wings (a) and resulting deformation (b)

7.3 Glass roof

As the doors are situated under a widely cantilevering building roof, no snow loads had to be taken into account. The glass roof is made of 3-ply laminated heat strengthened glass with sentry glass\(^{\circledR }\) interlayer. For verification, the roof is assumed to be supported only by the drum walls, taking into account the interlayer shear strength. Although the resulting deformation would be acceptable for standard overhead glazing, it is bigger than the tolerance provided by the turnstile support at the centre of the glass roof. As a result, the roof is being supported vertically by the turnstile whereas itself supports the turnstile for horizontal live and wind loads.

7.4 Connection of roof and drum walls

The roof rests on the upper drum wall edge with POM-C setting blocks placed between the two glass elements. The space between and around the setting blocks is filled with a structural bond to transfer the horizontal loads coming from the turnstile through the glass roof to the drum walls. Additionally, the glass roof connects all four drum wall segments improving the horizontal stiffness by a joint reaction.

7.5 Turnstile

The turnstile consists of four wings that are supported by U-shaped steel profiles along their horizontal edges. These profiles connect to each other at the upper and lower centre support, but there is no profile along the vertical edges and no centre axis. Thus, the glass wings are stressed by wind load, handling live load and dead load of the glass roof.

At the inner vertical edges, the glass wings are connected by structural bond filled in the box section in-between the glass edges (Fig. 13).

The bond was necessary to limit the wing deformation and to prevent the glass wings to collide.

A more detailed analysis had to be made as the handle was connected in the high stresses area causing stress peaks at the bore.

The U-shaped profiles along the horizontal edges provide support for loads normal to the glass surface, the vertical loads are transferred by setting blocks between steel profile and glass. The vertical support at the inner edge only causes horizontal forces along the horizontal edges. Therefore, a structural bond is applied between glass and profile. The bond is verified for permanent shear stress (Fig. 14).
Fig. 14

Door wing support profiles

7.6 Safety concept: residual load carrying capacity

As the glass members are used as primary support structure glass breakage must be taken into account. The glass roof is verified for one broken ply, two remaining intact, but without consideration of the turnstile support (safe side).

The drum walls are verified for two broken plies, one remaining intact for one of the four drum walls. All drum wall edges are protected against impact by steel profiles.

7.7 Materials

The US building owner uses German glass elements for many of his buildings, so there was no problem about the glass specifications, especially as the glass manufacturer could provide sufficient stress resistance values.

Surprising were the problems regarding the verification of the structural bonds. As it turned out, the applied product of the US-based producer, purchased in Europe, had no approval for the US market and it took comparison tests with an US-approved sealant of the same manufacturer to prove its applicability.

8 Summary

The door shown in Fig. 1b makes it obvious, that for a consistent safety approach it cannot be enough to limit the verification of revolving doors to its functional test requirements, but must be considered as a structural element as part of the façade, especially if taking into account that the revolving doors usually are used as main entrance doors passed by most people entering or exiting the building. Therefore, the answer to the initial question, whether revolving doors are machines or structural elements must—of course—be: both.

The two examples showed two different approaches to the structural verification of revolving doors for two quite different door types. The following headwords summarize the most important issues in the verification process according to the authors experience:
  • Safety and structural concept

  • Material data and approvals

  • Deformation criteria

  • Interaction with adjacent façade

Although standard doors “off the rack” do usually not comply with structural requirements, the technical, structural problems can usually be solved to everybody’s satisfaction if considered beforehand and with enough lead time to adapt the details to the structural requirements. Therefore, the timeline is the all-dominant issue with direct impact on the possible safety concept and design.

Notes

References

  1. ASTM E 1300: Standard practice for determining load resistance of glass in buildings (2016)Google Scholar
  2. DIN 18650-1: Powered pedestrian doors—part 1: product requirements and test methods (2010-06)Google Scholar
  3. DIN 18650-2: Powered pedestrian doors—part 2: safety at powered pedestrian doors (2010-06)Google Scholar
  4. EN 13830: Curtain walling—product standard (2015-07)Google Scholar
  5. EN 14351-1: Windows and doors—product standard, performance characteristics—part 1: windows and external pedestrian doorsets (2016-12)Google Scholar
  6. EN 16005: Power operated pedestrian doorsets— safety in use—requirements and test methods (2013-01)Google Scholar
  7. ETAG 002-1: Guideline for European technical approval of structural sealant glazing kits (SSGK)—part 1: supported and unsupported systemsGoogle Scholar

Copyright information

© Springer Nature Switzerland AG 2018

Authors and Affiliations

  1. 1.Ingenieurbüro Dr. SiebertMunichGermany

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