WO2018190705A1

WO2018190705A1 - Injected bolted connection

Info

Publication number: WO2018190705A1
Application number: PCT/NL2018/050217
Authority: WO
Inventors: Martin Paul NIJGH
Original assignee: Technische Universiteit Delft
Priority date: 2017-04-10
Filing date: 2018-04-09
Publication date: 2018-10-18
Also published as: NL2018677B1

Abstract

The present invention is in the field of an injected bolter connection, and specifically a new material therefore, such as for resin injected bolted connections, and a method for forming such a connection. A demountable, stiff, and slip-resistant connection is provided, such as a so-called double lap shear connection having two or more sheets or plates.

Description

Title Injected bolted con

FIELD OF THE INVENTION

The present invention is in the field of an injected bolted connection, and specifically a new material therefore, such as for resin injected bolted connections, and a method for form^¬ ing such a connection. A demountable, stiff, and slip-resistant connection is provided, such as a so-called double lap shear connection having two or more sheets or plates.

BACKGROUND OF THE INVENTION

The present invention is in the field of a connection for connecting a modular unit structure, such as plates, and foundation, such as concrete, and a construction method. In the foundation, such as a concrete plate, a relatively large vol- ume is provided, which volume is typically significantly larger that a volume of connection to be inserted through the volume in order to compensate a priori for potential mismatches in positioning of a plate on a foundation. Typically a connecting member is used for connecting the various elements, such as the modular unit structure and foundation concrete.

For example a plate may be connected by providing a mortar injection hole and an anchor bolt connecting hole. The plate typically has a regular thickness and a rectangular shape, and the mortar injection hole penetrates the plate and the founda- tion. The anchor bolt is then provided through the plate and foundation and fixed. Typically the free volume, surrounding the bolt, may then be provided with mortar or the like. Investigations have been performed to improve the characteristics of the filling material. Likewise the connection may be used for steel connections and the like.

Regulations regarding injection bolts may be found in EN 1993-1-8 and EN 1090-2. The first discusses calculation rules for design resistance of a connection with injected bolts, whereas the latter provides executional information on the de- tailing of the bolt and bolt hole itself. In principle, all fasteners of steel grades 8.8 and 10.9 that are allowed for preloaded and non-preloaded connections may be used in resin- injected bolted connections. Such fasteners may be found in respectively EN 14399 and EN 15048. In order to be able to in- ject the bolted assembly with resin, a hole is present in the head of the bolt. In case the bolts are designed to be preloaded, tightening should occur before the injection of the resin. In case of resin-in ected bolted connections, use of special washers may be prescribed under both the head and nut. The washers must typically fulfil the requirements of EN 1090- 2 Annex K. The washer under the head of the bolt promotes easy ingress of resin into the open space between bolt and plate package, whereas the washer under the nut includes a groove through which the air can escape during the injection of the resin. It is noted that fasteners used in pre-tensioned connections typically fulfil requirements prescribed in EN 14399. Therein, only bolts of property class 8.8 and 10.9 are allowed to be pre-tensioned. In order not to have problems regarding thread stripping, it is mandatory to leave a minimum of four threads sticking out at the free surface of the nut.

Static resistance of a connection may be measured according to EN-1090-2. Fatigue may be measured according to EN 1993-1- 9. Design resistance can be measured according to EN 1090-2.

The above connection find various purposes. Injection bolts may offer slip fatigue and shock resistant connections. Typically static load, slip, creep, and fatigue are used to qualify and quantify a connection. They can be used as an alternative to fitted bolts, rivets or preloaded bolts.

Injected bolted connections are used widely nowadays. Typi^¬ cally a resin is used for injection. However the resin is relatively expensive. In addition the resin has a relatively low stiffness, it is sensitive to creep.

The resistance of an injected bolted connection is considered to be based on a deformation criterion rather than on a strength criterion. The deformation criterion implies that the abovementioned effects of low stiffness and limited creep sensitivity are of great influence to a connections resistance.

Some documents recite connections, such as nails, such as US 2010/166505 Al and DE 2010 004381 Ul . US 2010/166505 Al recites a subsurface support is provided comprising a soil nail having an outer member and an inner member placed within the outer member. The soil nail includes features that maintain a uniform spaced relationship between the inner and outer mem- bers. The spaced relationship between the inner and outer mem^¬ bers may be achieved by crimping the outer member, or by use of an insert installed between the inner and outer members. The soil nail has two primary members, namely, an outer threaded member, and an inner threaded member that is placed through the outer member. The outer member is made from fiberglass, and a metallic drill bit is secured to a distal end of the soil nail. The inner member is preferably steel. The dual piece construction provides superior tensile and compressive strength, particularly for applications in which a coupler is used to join outer members to extend a length of the soil nail. Said soil nail is not particularly suited as a bolted connections, especially in view of forces applied thereto and further boundary conditions.

The present invention relates to an injected bolted connection, and specifically a new material therefore, and a method for applying such a connection, which overcomes one or more of the above disadvantages, without jeopardizing functionality and advantages.

SUMMARY OF THE INVENTION

The present invention relates in a first aspect to a connector according to claim 1. The connector is typically demountable, i.e. can be taken apart and parts can be reused. The connector provides an improved slip-resistance. It also provides a stiff connection. It has been found experimentally that the present connector is very stable over time, e.g. under application of for an intended use typical forces. It is also found that creep is significantly reduced. In addition it is also relatively cheap, e.g. cheaper than using only resin. It provides therewith a higher load capacity. In a way the connector may be regarded as a connecting system. To increase initial connection stiffness and decrease creep deformation of e.g. resin-injected connections with oversize holes, small, strong and stiff particles ( 'reinforcement' ) are added such as to the free volume within the connection, prior to injection of the bonding agent. The small particles are in direct contact with each other and fill most of the volume within the connection. For connections, such as double lap shear connections, a de^¬ mountable connection is formed with a higher (initial) stiffness and less creep deformation. The connection is immobilized by a fixing element. The fixing element may have a cross-sectional size of 2-120 mm, such as 5-100 mm. In order to fill a to be formed connection with resin an ¾ir escape channel may be provided to allow air to escape. In order to add load bearing particles a fill opening is provided. The fill opening typically has a cross-section 2-10 times larger than the (largest) particle size. The load bearing particles at least partially surrounding said fixing element, typically fully surround said fixing element, especially if the fixing element is located in a central part of the connector. The particles have a longest size, which may be the nominal diame^¬ ter, of 0.1-5 mm, such as 0.3-2.4 mm. They are preferably not too big, as load is less well distributed and particles are more difficult to add to the connector and more difficult to distribute over the connector evenly. The particles are preferably also not too small as they could become difficult to handle. To keep the particles in place and to provide a stiff connection a bonding agent is provided. Due to limited accessibility of free volume surrounding the fixing element, it is found somewhat difficult to introduce particles within this volume. The bonding agent may further prevent or mitigate external detrimental influences and/or it may increase an initial stiffness. Typically the bonding agent may need to be cured, such as chemically cured.

In a second aspect the present invention relates to a method of forming the present connector. Therein at least two sheets/plates of material (60,70) are provided, wherein at least one sheet (60) comprises a space for connection, placing the at least two sheets in contact with each other, providing the particles (30) and bonding agent (40), providing a fixing element (20) partly filling the space, fixing the at least two sheets, providing the particles into the space, injecting bonding agent into the space, and curing the bonding agent. Plates and sheets typically have a thickness of 1-500 mm, such as 2-50 mm and may be of any suitable length and width. If a sheet relates to e.g. a concrete floor a thickness thereof may even be much larger, such as 10-500 mm.

Thereby the present invention provides a solution to one or more of the above mentioned problems.

Advantages of the present invention are detailed throughout the description.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates in a first aspect to a connector according to claim 1.

In an exemplary embodiment of the present connector the particles have at least one of a spherical shape, a multigonal shape, and an irregular shape. As such many different shaped particles can be applied, such as irregular shaped grit or spherical shaped steel. Mixtures may be applied as well.

In an exemplary embodiment of the present connector the bonding agent is waterproof and/or weatherproof. Therewith good protection over time against environmental influences is provided.

In an exemplary embodiment of the present connector the bonding agent comprises one or more of a biocide, a fungicide, a UV-protector, and a corrosion protector. Therewith good pro^¬ tection against possibly detrimental species as well as against (UV-) light.

In an exemplary embodiment of the present connector the particles are made of a metal, such as of iron, of steel, such as shot steel, of a ceramic material, such as of natural stone, of gravel, of grit, and combinations thereof. Depending on factors such as the application, weight, type of bonding agent, environment, etc. a suitable material can be selected.

In an exemplary embodiment of the present connector the fixing element is at least one of a bolt, a head stud, and a shear connector. The present connector preferably is a removable connector, such as the above, which can be applied easily.

In an exemplary embodiment of the present connector the skeleton is a continuous skeleton, a continuously graded skel- eton, a gap graded skeleton, and combinations thereof. Depending on an application one or a combination of the above skele^¬ tons can be provided and the connector can be adapted thereto.

In an exemplary embodiment the present connector comprises an air escape channel (10), optionally wherein the air escape channel is the fill opening. For some application a separate air escape opening might be useful, e.g. the connector may be filled easier. For some application one opening, having a fill function and an air escape function, may be sufficient .

In an exemplary embodiment of the present connector the particles have at least two different sizes, preferably at least three different sizes, or wherein the size of the particles has at least one continuous size distribution, and combinations thereof. Not only can the filling be adapted in view of an application, but also can the filling be optimized therewith, e.g. in terms of relative amount of volume filled.

In an exemplary embodiment of the present method the connection is a shear connection, such as a double lap shear connection. The present invention is especially suited for these type of connections.

In an exemplary embodiment of the present method the space for connection is over-dimensioned with respect to the fixing element. Such may typically be the case, e.g. in order to prevent extra work to be done at a location where the connection is applied. Some extra space for a connection is then provided .

In an exemplary embodiment the present method further comprises removing the fixing element, the particles and cured bonding agent, separating the at least two sheets, and re-us^¬ ing the at least two sheets and optionally the fixing element.

The invention is further detailed by the accompanying figures and examples, which are exemplary and explanatory of nature and are not limiting the scope of the invention. To the person skilled in the art it may be clear that many variants, being obvious or not, may be conceivable falling within the scope of protection, defined by the present claims .

SUMMARY OF THE FIGURES

Figure 1 shows a schematic drawing of the present connector .

Figures 2a, b show a transparent connector.

Figure 3 shows a load-displacement diagram of shot-reinforced resin-in ected connection with 0_Centre = 32 mm and bolts positioned at most negative position in centre plate hole .

Figure 4 shows a connection slip at Centre Bolt Group (CBG) vs. time, indicating the creep deformation of shot-re- inforced resin injected specimen used in feasibility test.

Figure 5 shows a force-slip diagram for non-reinforced and shot-reinforced specimen (averaged) .

Figure 6 shows a slip-time diagram for non-reinforced and shot-reinforced specimen (averaged) .

DETAILED DESCRIPTION OF THE FIGURES

Figure 1 shows a schematic drawing of the present connector. Details of said figure are provided throughout the description. The small reinforcing particles are considered to form a continuous skeleton throughout the free volume within the connection, and hereby form a load bearing path. The resin acts more as a filler and bonding material. The particles transfer load through direct particle-to-particle contact, and reduce reguired resin volume, whereas the resin fills free volume, prevents sudden movement of particles, provides initial stiffness and protects particles against environmental influences.

EXAMPLES/EXPERIMENTS

The invention although described in detailed explanatory context may be best understood in conjunction with the accom- panying examples.

Experimental set-up

In order to assess the potential of reinforced resin- injected connections, a similar test on double lap shear connections is carried out as on the non-reinforced resin-in- jected connections. The resin is Araldite RenGel SW 404 + HY 2404, but the curing time thereof is reduced from 24 to 6 hours. The reinforcing particles used are so called steel shot particles, which are frequently used in shot peening, a process to remove residual welding-induced tensile stresses. An alternative to shot is grit : the latter may have an irregular shape, whereas the former is spherical. A reason to choose for spherical particles is their easy workability. Shot is available in many different size, ranging from 0 0.3 -2.4 mm. In a first experiment shot steel of size class S330 is used, which has a nominal diameter of 1 mm.

To establish the potential, a test specimen with 0_Centre=32 mm is prepared. As opposed to other specimen, the specimen for this test has been assembled in what may be considered as the most negative position for connection slip in the centre plate (totally of centre) . The bolt is directly bearing to the cover plates. The connection build-up has an injection length linj of 12 mm, which is 3 mm ( + 33%) more than the specimen with

mm as tested for non-reinforced resin- injected connections with oversize holes. The specimen is loaded to a load level belonging to 0.15-0.20 mm slip at CBG, and the load is kept constant in order to determine creep sensitivity of the shot-reinforced resin-injected connection.

In an example a transparent sample connection is made using Perspex plate elements. The shot is inserted through an air escape channel in the centre plate. Simultaneously, the shot within the connection is compacted by vibrating the specimen using a hammer and more shot is added until the specimen is completely filled. The result of this step is illustrated in Figures 2.

After filling the specimen with shot, resin is injected through the hole in the bolt head. Although the voids in between the shot particles is relatively small, no additional effort for the injection process was necessary and all voids were filled with resin.

Results

The test results from the shot-reinforced resin-injection with geometry are presented in Figures 3-4. Figure 3 illustrates a load-displacement diagram obtained during loading the specimen to a load belonging to an initial average slip at

CBG of 0.19 mm (159 kN) , whereas Figure 4 shows the subsequent creep behaviour.

The initial connection stiffness (defined between 0.05 and 0.15 mm connection slip) is kisi = 800 kN/mm, with a spread of ±5%. The average spread in the creep-phase is 3%. It has been found that not only the oversize hole in the centre plate was filled with shot, but also the small volume between the bolt and hole in the cover plate was saturated therewith.

The experimental initial connection stiffness kini for the shot-reinforced resin-injected connection is double (0200%) that of the numerically obtained initial connection stiffness for a non-reinforced connection. The load level during the creep test was 159 kN, which leads to a nominal bearing stress of Gb = 199 Pa. The slip after 50 years is not expected to be larger than 0.30 mm, given that the tangent of the slip curve is smaller than that is needed to reach the coordinate [50y, 0.30 mm] . This conclusion could already be drawn after roughly 10³ minutes (17 h) , but the experiment was continued for several days to see the development of creep deformation in time. The use of shot-reinforced resin-i ected connections with oversize holes seems promising. In the case of the shot-reinforced connection, a nominal bearing stress Ob = 199 MPa is rather high compared to the bearing stress of non-injected connections (Ob = 9 MPa for non-reinforced connection with 0_Centre = 36 mm) . Moreover, the results of the shot-reinforced connection were obtained using l±_nj = 12 mm, whereas this was maximally linj = 9 mm for the non-reinforced connection (for 0_Centre = 36 mm) . Although the amount of connections tested is limited (n = 2), shot-reinforced resin-injected connections reduce creep and increase connection stiffness compared to non-reinforced resin-injected connections.

Comparison between shot-reinforced and non-reinforced resin-injected specimen under same conditions

The behaviour of shot-reinforced and non-reinforced resin- injected connections is compared. In order to see the difference in initial and time-dependent behaviour, a shot-reinforced resin-injected specimen with 0_C6ntre =36 mm is prepared under the same conditions (i.e. position of the bolt with respect to the holes) as done for the non-reinforced resin-injected specimen (also 0_Centre =36 mm) . The shot-reinforced specimen is loaded using a force-controlled regime (0.2 kN/s) until an average CBG slip of UCBG = 0.135 mm (90% of the short- term strength based on a 0.15 mm slip criterion). At the moment the average slip of 0,135 mm at CBG is reached, the force is kept constant in time.

The table below summarizes the above results. Initial connecSlip creep deformation after., (mm)

Connection Long-term load

tion stiffness

Type F_LT (kN)

ktni (kN/mm) 24h 48h 72h

Non-rein¬

5,8^■ 10² 75,2 0,0584 0,0677 0,0719 forced

Shot-rein9,9^■ 10² 140 0,0381 0,0422 Not meaforced (+71%) (+86%) (-35%) (-38%) sured

Example of application for the present conncetion may be found in the Maeslant Storm Surge Barrier and in the Schloss- briicke Oranienburg (Germany) . In the barrier a force of the water on the gates can be as large as 36 MN, which has to be transferred through a truss to the system's ball bearing into the foundation. In order to prevent connection slip at the connection between the truss and ball bearing, resin-injected preloaded bolts have been used of metric sizes M56, M64, M72 and even M80. The main reason for such large bolt sizes is that the plate package is rather thick, and the contractors wanted to stay within the range I/d≤3. For the bridge numeri- cal research has shown that replacement of rivets used with injection bolts leads to an increase of load transferred by the rivets, which is considered mainly related to the relatively low stiffness of the resin. In case the resin does not fully fill the cavity between the hole and bolt (e.g. due to too little injected resin, too high resin viscosity) , the differential load distribution is aggravated.

Claims

1. Injected bolted connector (100) comprising

a fixing element (20) ,

load bearing particles (30) at least partially sur^¬ rounding said fixing element forming a skeleton, the particles having a longest size of 0.1-5 mm, such as 0.3-2.4 mm,

a bonding agent (40) at least partly surrounding said particles for forming a stiff connector selected from glues, resins, adhesives and combinations thereof, and

a fill opening (50).

2. Connector according to claim 1, wherein the particles have at least one of a spherical shape, a multigonal shape, and an irregular shape.

3. Connector according to any of the preceding claims, wherein the bonding agent is waterproof and/or weatherproof.

4. Connector according to any of the preceding claims, wherein the bonding agent comprises one or more of a biocide, a fungicide, a UV-protector , and a corrosion protector.

5. Connector according to any of the preceding claims, wherein the particles are made of a metal, such as of iron, of steel, such as shot steel, of a ceramic material, such as of natural stone, of gravel, of grit, and combinations thereof.

6. Connector according to any of the preceding claims, wherein the fixing element is at least one of a bolt, a head stud, and a shear connector.

7 . Connector according to any of the preceding claims, wherein the skeleton is a continuous skeleton, a continuously graded skeleton, a gap graded skeleton, and combinations thereof .

8. Connector according to any of the preceding claims, comprising an air escape channel (10), optionally wherein the air escape channel is the fill opening.

9. Connector according to any of the preceding claims, wherein the particles have at least two different sizes, preferably at least three different sizes, or wherein the size of the particles has at least one continuous size distribution, and combinations thereof.

10. Method of forming a connector according to any of the preceding claims comprising

providing at least two sheets/plates of material (60,70), wherein at least one sheet (60) comprises a space for connection,

placing the at least two sheets in contact with each other,

providing the particles (30) and bonding agent (40), providing a fixing element (20) partly filling the space ,

fixing the at least two sheets,

providing the particles into the space,

injecting bonding agent into the space, and curing the bonding agent.

11. Method according to claim 10, wherein the connection is a shear connection, such as a double lap shear connection.

12. Method according to any of claims 10-11, wherein the space for connection is over-dimensioned with respect to the fixing element.

13. Method according to any of claims 10-12, further com^¬ prising

removing the fixing element, the particles and cured bonding agent,

separating the at least two sheets, and

re-using the at least two sheets and optionally the fixing element.