How to perform NSCE and NLKA checks

This guide contains the procedures for the assessment of the non-seismic structural elements (NSCE). Part of that assessment is performed with the non-linear kinematic analysis, which is treated in a separate part in this guide. This guide is maintained by the task force NSCE and the task force NLKA. If you have any questions while performing these procedures, please use the teams channel NLKA and NSCE.

Warning

The NLKA method shall not be performed for the cantilever walls with slenderness (height over thickness) 20 and greater. Therefore, any NLKA results are NOT valid for the following cases:

• Cantilever wall with a height of 4.2m and greater (thickness 0.21m).

• Cantilever wall with a height of 2m and greater (thickness 0.1m).

Those walls will collapse during an earthquake unless demonstrated otherwise.

The following diagram demonstrates how to handle the assessment for the different elements and which tools are available within VIIA.

Figure 111 Diagram of the NSCE and PSSE assessments and tools.

NSCE assessment

For NLTH and NLPO-SDF the workflow is the same for the NSCE. The workflow is shown in the figure underneath. The steps are explained in this guide.

Figure 112 Workflow for the NSCE assessment in the VIIA project.

• It is important to model the NSCE since as a strengthening measure a floor can be connected to a non-load bearing wall, transforming it in a load bearing wall, thus it becomes a PSsE.

• Also a non-load bearing wall can provide cantilever effect on the out-of-plane behaviour of a perpendicular wall (1-way or 2-way bending) avoiding it’s failure.

Step 1 - Identify NSCE

Within a building, elements can be categorised in following three groups according to the NPR:

• PSSE: Primary and secondary seismic elements (Primaire and Secundaire Seismische Elementen)

• NSCE: Non-seismic structural elements (Niet-Seismische Constructieve Elementen)

• NCE: Non-structural elements (Niet-Constructieve Elementen)

A further explanation about PSSE, NSCE and NCE is given in the Basis of Design.

This step is to identify the non-seismic structural elements in the building. These are drawn on a floorplan of the building. The colours are indicating the different element types of the NSCE’s. This drawing is part of Appendix C2. An example of such a floorplan is given in Figure 3.

Figure 113 Example drawing in Appendix C2.

An example of the template of Appendix C2 is available here: LINK.

Step 2 - Main steps in the NSCE assessment

There are three main steps in the NSCE assessment:

• Determine if the element needs assessment, based on the potential lethal hazard criteria and the occupancy criteria;

• If yes in the point above, determine which NSCE category is applicable;

• Perform the assessment (capacity vs demand).

Step 3 - Check for potential lethal hazard

Refer to NPR 4.3.6.1 condition 1 to verify if there is any potential lethal hazard.

Non-seismic structural elements shall be considered if both the potential lethal hazard criteria and the occupancy criteria apply:

Condition 1: If the falling mass of the NSCE element or a part thereof is greater than 1 kg, and one of the following three conditions is satisfied, the NSCE needs to be further assessed:

1. Vertical elements or parts thereof with a mass per area unit of less than 60 kg/m² where the fall height from the bottom of the element, or the part thereof, to the adjacent floor or the adjacent area exceeds 2.0 m or the distance from the top of the element, or the part thereof, to the floor or the adjacent area exceeds 3.0 m. * Note that for a 100 mm thick masonry wall the weight is 200kg/m² .

2. Vertical elements or parts thereof with a mass per area unit equal to or greater than 60 kg/m² where the fall height from the top of the element, or the part thereof, to the adjacent floor or the adjacent area exceeds 1.2 m.

3. Horizontal elements, if the mass per unit area exceeds 25kg/m² .

Step 4 - Check the criteria for occupancy

Condition 2: Refer to NPR 4.3.6.1 condition 2 to verify the occupancy at the location where the risk occurs: the element can fall in a location where there is a significantly high probability of one or more people being present there during an earthquake. An element complies with this condition if, in the event of full or partial collapse, every part of the element, viewed in the horizontal cross section over the length of the element, might fall in or on points 1 to 4 of the next table.

Some walls that might fall outside also might fall inside, thus criterion A of the following table is satisfied, therefore there is no need to check criterion 1 to 4.

Figure 114 Table occupancy criteria.

• a ground plane projected perpendicularly for the falling element within 1 m on either side of an entrance or exit of a regularly occupied building (measured horizontally parallel to the relevant façade) along a distance equal to the provisions of a), measured perpendicular to that entrance or exit.

• is located inside a building intended to be used by people, or could fall from a height of 2 m or more onto the roof of any part of a regularly occupied building.

Note

If the failing element is falling into a space that is an escape route, assessment is required.

Figure 115 Wall types that require assessment.

Step 5 - Determine category of NSCE

Refer to NPR table 2.2 to determine the category of the NSCE element.

The next flowchart presents different situations and the following paths which lead to choosing the adequate category for the Non Structural Seismic Element.

Figure 116 Categories flowchart.

For Category 4 the 2475 return period, for Category 3 the 975 return period, and for Category 2 the 475 return period shall be applied.

Description of flowchart notes

1. Examples of less hazardous elements are: stairs in single family homes and glazing other than curtain walls.

2. Escape route or entrance area:

   • All doors, also doors to a garden/terrace + 1 m on both sides of them (defined as normally entrances and escape routes used during fire);

   • Outdoor escape route: only if it is not possible to escape at about 2 to 3 meters distance from the building (this includes pathways to escape from).

3. Publicly accessible outdoor areas: includes both situations:

   • Outdoor areas on the private property of the building which are open for public use by visitors to, or customers of, facilities in the

   • Building such as restaurants, theatres or museums, and;

   • Outdoor areas on public property such as streets, squares, bicycle paths, or roads where people might be put at risk by congregating outside or walking/cycling/driving past the building.

   Note

   Clarification of the criterion 1 to 4 of NPR 4.3.6.1 ‘Condition 2’ a):

   

   Figure 117 Scheme of the criterion.

4. Well-frequented: only sitting areas of bars/restaurants or similar and (reasonably busy) shopping streets, ‘voetgangersgebied’ -> pedestrian area in city centers or similar. Streets where the cars pass usually are not so crowded by pedestrians so are not included here.

5. Normally frequented: Other situations.

6. Service functions: Assembly** functions, healthcare functions, residential functions for 24/7 care, education functions and comparable forms of use.

7. Residential functions: houses/apartments excluding residential functions for 24/7 care, lodging functions, office functions and comparable forms of use.

8. Connected on top: A wall is considered well connected on top if the connection is reliable enough to resist a seismic action, if this is true then YES applies, if not, is NO.

   Note

   Clarification of the surface area of the element:

   Area of the horizontal projection on a vertical plane or of the vertical projection on a horizontal plane of a failing element.

   

   Figure 118 Surface area o the elements.

Step 6a - Case of chimneys

All chimneys are category 4 if they fall on an area as described below:

• Within the floor surface of the building;

• Or from the outside on the roof, when falling from more than 2.0 m.

Figure 119 Figure 9 - Fall height of the NSCEs.

Note

Normally a chimney is assumed to roll of a roof and not fall through it.

• During the earthquake, in case of sloping roofs, the chimneys are assumed to roll from the roof and not to fall inside the floor area.

• The following pictures show the probability of the chimney to fall in different locations of the building depending on the type of roof.

• For our TVA’s, these pictures are relevant to determine which areas should be considered to be are at risk.

Figure 120 Scheme of the probability of the chimneys falling into certain areas due to their location in the roof.

All chimneys are category 4 if they fall on an area as described below:

• In the escape route (ingress or egress) or entrance area (the element, or part of it, can fall within 1m of any part of the route). For example:

• In the figure the red chimney would fall within less than 1 m next to the door so this chimney would be -> Category 4;

• On the other hand, the blue chimney would fall in a distance superior to 1 m regarding the access door, thus would be checked, considering its area, and its location (well-frequented area vs normally frequented) to determine its category.

Figure 121 NSCEs and egress routes.

If the chimneys are not falling in the situation described previously (Category 4), then:

• Large chimneys with a projected area A > 10 m² :

  • If falling in publ.acc.out.areas -> Category 4

• Medium sized chimneys with a projected area 3 m² < A < 10 m² :

  • If falling in well-frequented publ.acc.out.areas -> Category 4

  • If falling in publ.acc.out.areas -> Category 3

• Small chimneys with a projected area A < 3 m² :

  • If falling in well-frequented publ.acc.out.areas -> Category 3

  • If falling in publ.acc.out.areas -> Category 2

Step 6b - Case of gable walls

It shall be considered that the gables are connected sufficiently to the upper element (roof, gutter, etc.). Therefore, those will not be cantilevering. This is valid for single leaf walls as well as inner and outer leaves of the cavity walls.

In order to choose the proper category, the surroundings around the falling area need to be assessed.

• If the walls are falling inside the building, then should be -> Category 4

• If they fall outside next to an escape route or pathways should be -> Category 4

• If the walls fall from a height superior to 2 m to another part of the building should be -> Category 4

• If walls fall away from escape routes or pathways, then their category should be judged by their surface area -> (Categories 4, 3 or 2)

The following workflow can be applied to the objects assessed.

Step 6c - Case of non-load bearing leaves

The cavity walls shall be assessed based on the analysis method: NLTH-REF/NLPO-REF, NLTH, and MRS/NLPO. There are two flowcharts for each method, however, the flowcharts with ‘Preferred way of working’ label shall be applied by the structural engineers. Please read the following paragraphs and terms in advance.

The upper boundary condition: It shall be considered that the outer leaves are connected sufficiently to the upper element (roof, gutter, etc.). Therefore, those will not be cantilevering.

OOP Assessment: The term refers more in general to the NLKA/virtual work method using the L4 tool. It is expected that the engineer knows how to perform the assessment, how to perform the 1-way or 2-way spanning depending on the particular case. In order to decrease the computation time, a good practice is to start with the 1-way spanning assessment, and eventually proceed with the 2-way spanning assessment if necessary. When all the possible situations that represent the wall analysed have been performed, the assessment can be considered concluded.

Retrofit: The term refers in general to the right measure for the case, based on the GMC database. Retrofit is intended as the more cost-effective measure that can prevent failure of the element. In order, the retrofitting measures to apply are assumed: connections (top and/or bottom), cavity wall ties, out-of-plane measures (L4 measure).

Check of the retrofit: Each proposed measure has to be explained and the results verified. If for example the first assessment of a cavity wall without ties leads to failure, cavity ties are the first measure to be proposed. If the assessment of the retrofitted wall fails again, a further measure has to be proposed (and verified).

Figure 122 Flowchart preferred way of working for NLTH-REF and NLPO-REF.

Refer to document VIIA_QE_R2037.

Figure 123 Flowchart preferred way of working for NLTH.

• Modelling in DIANA: To connect the outer to the inner leaf, in DIANA two approaches can be followed:

  • Apply wall ties along the line of the connection viia_create_wall_ties_on_line().

  • Model a roof plate at the top of the element and a D2.01 line interface.

  • Create a dummy plate between inner and outer leaf (not recommended, due to the local axes).

• Modelling in ABAQUS: In ABAQUS ties should be modelled explicitly.

** The NLTH results for a 2-storey building showed that cavity walls with 2 ties/m²(considered case of high possibility of corrosion) and 4 ties/m²(in general >1990) possessed comparable capacity. It is considered that this conclusion also holds for cavity ties 1.67 ties /m²as per section 9.2 of NCG-ABSC version 1.2. In case of less cavity ties or highly corroded cavities ties, it is recommended to apply measure L4-D.

*** Measure L2-051 (renovation anchor) at floor level, if ties are already present, is generally not necessary.

The outer leaf can be included in the determination of the resistance of the cavity wall if all the following the conditions are met:

• It has been proven that sufficient reliable cavity ties are present;

• It has been proven that sufficient reliable cavity-ties or anchors (or another connection) are present at the level of the diaphragm (roof or floor) to connect the outer leaf to the diaphragm as a horizontal support.

• If anchors are used, it should be verified whether sufficient displacement capacity is available to cope with thermal movements.

Use the proper version of the L4-sheet in order to take into account the contribution of the outer leaf to the seismic capacity of the wall.

The category of the non-load bearing outer leaves in a cavity wall can be determined as follows:

• If the walls are inside the building, they should be -> Assessed as partition walls;

• If walls fall outside next to an escape route or pathways -> Category 4;

• If they fall from a height superior to 2.0 m to another part of the building -> Category 4;

• If they fall away from escape routes or pathways, then their category should be judged by their surface area -> **Categories 4, 3 or 2.

Figure 124 Scheme of spanning ways of the walls.

Step 6d - Case of partition walls

If the partition walls have a maximum thickness of 100 mm and a maximum height of 3,0 m they can be inserted in different categories.

• If the walls are inside a 24/7 care, lodging functions, office functions and comparable forms of use, service functions in general:

  • Adequately connected on top -> Category 3

  • Not adequately connected on top -> Category 4

• If the partition walls are inside a residential functions building:

  • Adequately connected on top -> Category 2

  • Not adequately connected on top -> Category 3

• Partition walls (or other vertical NSCE elements) with a mass < 60 kg/m² -> Do Not Need Assessment.

• In general, aerated concrete and gypsum block walls up to 70 mm thickness should be < 60 kg/m² -> Do Not Need Assessment.

• Exception is when wall < 60 kg/m² and height > 3.0 m, then it should be assessed as an NSCE -> Category 4.

  Note

  • HSB partition walls generally will pass because of their small mass resulting in a low seismic demand.

  • That brick walls already from t=50 mm have mass > 60 kg/m² (≈100 kg/m² ).

• Partition walls (or other vertical NSCE elements) with a mass > 60 kg/m² with falling height of top of element < 1,2m -> Not Need Assessment.

• Partition walls t > 100 mm and/or h > 3.0 m -> Category 4.

Step 7a - Generic risk assessment

For chimneys, spandrels and gable walls, the generic risk assessment can be performed. Refer to NPR9998:2018 appendix J.

• Occurring PGA (‘demand’):

  • Choose the a_gS (g) corresponding to 475 years for the specific location (Webtool)^* .

• Maximum allowable PGA (‘resistance’):

  • Determine the member type;

  • Determine the category;

  • Go to Table 1 in the Protocol (How to perform NSCE and NLKA checks) or Table 9-10 UPR 05/2021;

  • Get the value of a_gS (g) corresponding to the NSCE category and Type.

    Occurring PGA < Maximum allowable PGA -> OK

    Occurring PGA > Maximum allowable PGA -> FAIL proceed with Semi-probabilistic assessment

• Table 1 gives the maximum PGA allowed for a certain element.

Table 1 - Maximum peak ground accelerations in [g] for chimneys, spandrels and gable walls.

Type of NSCE \ NSCE Category	2	3	4
Chimneys and parapets, freestanding walls and balustrades pre 1920	0.149	0.114	0.078
Chimneys and parapets, freestanding walls and balustrades from 1920 onward	0.207	0.164	0.118
Gables, pre 1920	0.283	0.248	0.203
Gables, from 1920 onward	0.298	0.263	0.217

^* Check the peak ground acceleration a_g S for the location of the building on the webtool. If the value in the table is higher, the element complies.

Attention

Please the use the a_g S of the 475 return period from webtool to compare with the capacity of the corresponding return period of the NSCE category.

Example: When you have a gable built in 1930, which is category 4 NSCE element, according to Step 4 the return period is 2475 year, then the capacity you get from the table is 0.217 g. Then you check the webtool for the 475 return period a_g S for the assessment, if the a_g S is lower than 0.217 g, then this element complies.

Step 7b - Semi-probabilistic assessment

Other elements than chimneys, spandrels and gable walls should be assessed with the semi-probabilistic assessment tools.

Tool for the semi-probabilistic assessment for masonry: Guidelines for NLKA tool

Tool for the semi-probabilistic assessment for other materials: Tool

Warning

The tool for other material is currently available in the teams channel for NSCE and NLKA. They still need validation by the knowledge team or will be later updated on the assessment method from knowledge team.

NLKA for PSSE assessment

For existent buildings, the application of conservative code requirements (elastic domain) required for new building may turn into expensive retrofitting solutions, this has been observed in earlier modal analysis assessments with out-of-plane (OOP) seismic actions calculated from the linear elastic analysis (LEA). The seismic resistance based on stability mechanisms rather than static strength, where a cracked URM wall is modeled as rocking rigid blocks, is less conservative and closer to the actual behaviour of unreinforced masonry. A kinematic approach is proposed in the NPR. The NLKA assessment (Non-Linear Kinematics Analysis) is used to determine the out-of-plane behaviour of unreinforced masonry elements (walls, gables, etc).

The upper connection of the walls that are classified as ‘high’ (h_wall≥7m and distance to the perpendicular support ≥ 5m) shall be checked carefully. If the wall is connected sufficiently to the upper element, the NLKA method can be applied otherwise; an L2 measure shall be used at the top. Afterward, the NLKA method can be applied. The following figure shows an example of a ‘high’ wall.

Figure 125 Definition of a ‘high’ wall.

Regarding the cavity walls, the floors and the cavity wall ties determine the height of the inner and the outer leaves. If the timber/concrete floor is not resting on the outer leaf and the outer leaf is not connected to the inner leaf with ties/anchors, it spans the whole height. Otherwise, it spans from floor to floor.

The tool used to perform the NLKA analysis on masonry elements is the Excel Tool: L4 spreadsheet. For application with NPR9998:2018+C1+A1:2020 you should use version 6.9 of the tool ( LINK NPR2018_v6.9) . For application with NPR9998:2020 you should use version 7.7 of the tool ( LINK NPR2020_v7.7) or version 8.0 ( LINK NPR2020 v8.0). If the non-load bearing leaf contributes to the seismic capacity of the load bearing leaf, the last version of the tool shall be used.

Guidelines for NLKA capacity graphs

In the case of one-way spanning unreinforced masonry walls the out-of-plane seismic demand could be obtained by using the NLKA method. This demand together with the resistance of the wall can be used to derive the maximum allowed height of a wall by checking for which height the unity check will be equal to 1 (or just below 1). This can be done repeatedly for different sets of parameter combinations after which it can be visualised with a graph showing curves for these different combinations of parameters. The curves on the graph show a maximum wall height versus the overburden load for specific boundary conditions. Each individual curve represents a specific combination of generalized values for the center of gravity over height ratio (z/H) and the building period (T_eff). The figure below gives an example of such a graph.

Figure 126 Maximum heights one-way spanning wall for boundary conditions 1-5

The graph needs some explanation in order to understand it and for it to be of use to the engineer. The data points in any of the curves shown in the graph represent the maximum height of a wall under a certain overburden load, z/H ratio and T_eff for which the wall still complies to the seismic demand. It should be noted that the boundary conditions of the wall, for example BC 1 and 5, also have an impact on the seismic demand and therefore the curves. However, the BC’s are always the same for all curves on the graph. If the engineer observes a wall in their building that for the applicable parameters would represent a data point above the corresponding curve, this would represent a failure of the wall for the out-of-plane assessment.

In some cases, combinations of the parameters z/H and T_eff yield the same result for the maximum heights. For this reason only one curve is plotted in the graph instead of multiple. The different combinations of z/H and T_eff that lead to the curve are combined in a range of values that is shown in the legend for that particular curve. All graphs are ‘cut-off’ at a 8.0 m height of the wall if applicable. It is assumed that in reality most walls are not higher than 8.0 m, thus making the results with maximum wall heights above this value irrelevant. Therefore, curves that are completely above the 8.0 m cut-off are not plotted. Instead the note beneath the graph will inform the engineer about the parameter combination(s) that produce(s) a curve that is not plotted.

Example: Take the curve from the first entry in the legend of Figure 18. If the z/H ratio is 0.1 and the T_eff is in the range of 0.3 s to 0.6 s or if the z/H ratio is in the range of 0.3 to 0.9 and the T_eff is 0.3 s, the dark blue curve is the result for the maximum allowed heights. If, for example, a wall in your building is 3 m high, has an overburden load of 2 kN/m, a z/H ratio of 0.5 and a T_eff of 0.3 s, the data point that would represent this input would lie above the dark blue solid curve. Therefore, the engineer can directly conclude that there is failure in this wall. See figure below for the visualization with the red dot representing the data point described above.

Figure 127 Out-of-plane failure of wall if data point, represented by the red dot, is above the applicable curve.

The goal of these location specific capacity graphs is to preemptively assess whether certain unreinforced masonry walls in a building are going to fail out-of-plane. If so, the engineer can choose, in consultation with the lead engineer, to apply pre-measures to the wall. This can save analysis time and speed up the assessment process.

The graphs will be generated automatically when creating the project. This is done only once to save runtime in later use of your modelscript or mainscript. All the necessary graphs will be generated, but if desired it is possible to generate (an) additional graph(s). This can be done by using the _viia_nlka_graph_data() function with the parameters the engineer desires.

project.viia_nlka_graph_data(
    e_top=1,
    e_bottom=5,
    thickness=0.1,
    material_name='MW-KLEI<1945',
    return_period=2475,
    z_over_height=[0.1, 0.3, 0.5, 0.7, 0.9],
    building_period=[0.3, 0.5, 0.6])

Note: Both the the z_over_height and building_period function arguments could be asigned as a singular value but should be provided in the format of a list containing that value.

Guidelines for NLKA tool

Attention

Several third-party packages are needed for this tool to work, they are as follows:

Matplotlib PyQt5**| **fpdf

Please make sure you pip installed these packages before you use this tool.

You can find template_NLKAscript.py in the folder of templates in viiapackage. Please save a copy of this python file in your work folder. Afterwards please change the object name without “-model” at the end. Only in this way can the data from database be retrieved as inputs for NLKA tool.

Now if you run this script, you will see the window below popping up on your screen.

Figure 128 NLKA tool initial window.

Because currently there are objects using the NPR9998:2018 and the NPR9998+C1+A1:2020 , you need to choose between this two options. Confirm this with your project leader if you are not sure.

Once you select and click OK button, you can see the following window pops up. The options for boundary conditions and the picture for table H.1 will be different if the NPR9998+C1+A1:2020 is selected.

Figure 129 NLKA tool interface NPR9998:2018.

Figure 130 NLKA tool interface NPR9998+C1+A1:2020.

Explanations for the parameters are as follows:

• Elment name

  Element with numbering at its end, by clicking Generate new name a new name will be generated, be careful that by using the same name the report of the same element name will be replaced.
• The height of the URM wall

  The height of the masonry element. If you have question about the height of triangle wall, please check the question of triangle wall.
• The thickness of the URM wall

  The thickness of the element. If you have question about the cavity wall, please check the question of cavity wall.
• The behavior factor

  The element behaviour factor, qa = 1 for cantilevers and qa = 2 for vertical spans and gables. If you have question about cantilever element, please check the question of wall not in the spanning direction.
• The height of the centre of gravity of the wall to the top of the foundation

  As is stated.
• The total height of the building

  The height of the building above top of the foundation or rigid basement
• The overburden load acting on the wall

  The overburden load acting on the wall per meter.
• Density of the material

  As is stated.
• Peak ground acceleration from webtool

  As is stated. Check the peak ground acceleration a _g S for the location of the building on the webtool.
• The fundamental period of the vibration of the building

  As is stated. If you have question about the frequency of the building, please check the question of frequency.
• Is the element NSCE or PSSE

  As is stated. When NSCE is selected, the importance factor will always be set at 1.0. When PSSE is selected, You have to give the consequence class of the object so that the right importance factor will be used to multiplied

  Note

  In Table 2.4 of the NPR is mentioned that for elements of category 4, that fall from a relatively great height onto an adjoining roof under which there can be people, the importance factor should be 1.2.

• Consequence Class

  As is stated. You can check the consequence class of your object from MYVIIA or consult with your project manager.
• Is the element a chimney?

  As is stated. If yes is selected, the overburden load row will be switched to zero, this option is only shown if the Cantilever behavior factor is selected.

Explanations for boundary conditions are as follows:

• Eccentricity at the top of the wall
  • For NPR9998:2018, 1, 2 or 3 can be selected if behavior factor 2 is selected, 6 or 7 can be selected if behavior factor 1 is selected, please check table H.1 for more explanation.
  • For NPR9998+C1+A1:2020, 1, 2 or 3 can be selected if behavior factor 2 is selected, 6, 7 or 8 can be selected if behavior factor 1 is selected, please check table H.1 for more explanation.
• Eccentricity at the bottom of the wall
  • For NPR9998:2018, 4 or 5 can be selected if behavior factor 2 is selected, 8 can be selected if behavior factor 1 is selected, please check table H.1 for more explanation.
  • For NPR9998+C1+A1:2020, 4 or 5 can be selected if behavior factor 2 is selected, 9 can be selected if behavior factor 1 is selected, please check table H.1 for more explanation.
• Angle θ (interstorey drift)

  The inclination angle of the element. For the NPR9998+C1+A1:2020, θ _v is shown here. θ _v in NPR9998+C1+A1:2020 corresponds to θ in appendix H of NPR9998:2018. If you have question about the inclination angle, please check the question of inclination angle.

How to select proper boundary conditions for your elements:

• As per Table H.1 there are two possible schemes for wall element -
  • One-way vertically spanning walls
  • Cantilever or Gable or End walls
• One-way vertically spanning walls

  There are three possibilities for eccentricity at the top - 1, 2, and 3.

  • Boundary condition 1 is used if there’s a rigid floor resting on top of the wall.
  • Boundary condition 2 is used if there is a timber floor resting on the wall and the floor beams of the timber floor are transferring loads at the center of the wall cross section.
  • Boundary condition 3 is used, if floor joists are fixed to the face of wall (this is the case when the wall-floor intersection is parallel to the floor spanning direction) and are not embedded in the wall.

  There are two possibilities for boundary condition at the bottom - 4 and 5

  • Boundary condition 4 is used if there is a rigid concrete foundation or a rigid slab located below the wall. The boundary condition 5 is used conservatively if a shallow (masonry footing) is present below the wall.

Boundary condition 4 may be used also for masonry strip footings when a minimum foundation geometry is observed (footing width ‘B’ and block height ‘hf’). To determine the minimum geometries for clay like soil and sand like soils and walls of 100 mm and 210 mm of thickness use the following 3 images. Notice that for 100 mm clay brick walls in sand like soils BC=4 can be directly assumed. The seismic intensity ‘Sae’ corresponds to the value of ‘SEa;d’ as defined in the NPR section H.3.1.

Figure 131 Minimum foundation block geometry for fixation in clay like soils and 100 mm clay brick walls (Sae=seismic intensity).

Figure 132 Minimum foundation block geometry for fixation in clay like soils and 210 mm clay brick walls (Sae=seismic intensity).

Figure 133 Minimum foundation block geometry for fixation in sand like soils and 210 mm clay brick walls (Sae=seismic intensity).

‘Sae’ can be extracted from the L4-sheet alternatively (SEa;d in the sheet). Please consider that the extracted intensity shall be divided by 10. Therefore, from the following results, 0.3344 [g] must be used, for instance.

100 mm clay brick walls graphs shall be used for cavity walls. However, for calculating ‘B’, both leaves must be taken into account. See the following example in which the outer leaf is assessed.

B (650 mm), hf (590 mm), and Df (690 mm) can be found from the figure and Sae (0.27 [g]) from the L4-sheet. For this case we can use the thicker solid black graph: Sae=0.3, Df=0.5m.

Firstly, find the intersection of “B” and “hf’ as follows: Point A. Then extend the Sae graph by extrapolating ‘B’ and ‘hf’ (dotted line in the following figure). If Point A is located on the right-hand side of the Sae graph, choose rigid boundary condition for the outer leaf of the cavity wall. See the following figure.

Some examples are provided to assist in the selection of the boundary conditions:

Figure 134 Example selection of boundary conditions (Check the minimum foundation block geometry graphs to identify if it is 4 or 5).

Whenever in presence of a cavity wall with ties, with outer leaf spanning two storeys, it has been demonstrated that the wall can be split at floor level. The boundary conditions for both cases and both leaves are B.C. 2 at the top and 4 at the bottom.

Figure 135 Example of cavity wall with ties, with outer leaf spanning two storeys.

• Cantilever and gable or end walls (As per NPR 9998: 2018)

  There are two possibilities for eccentricity at the top - 6, and 7.

  • Boundary condition 6 is used, when the roof purlins are pocketed into the wall and load is applied at the center of the wall cross section.

  There is only one possibility for eccentricity at the bottom - 8.

  • Boundary condition 7 is used when purlins are fixed to the face of the wall (this is the case when wall-roof intersection is parallel to the roof spanning direction) and are not embedded in the wall.
• Cantilever and gable or end walls (As per NPR 9998: 2020)

  There are two possibilities for eccentricity at the top - 7 and 8.

  • Boundary condition 7 is used if there are purlins embedded in the wall such that they transfer vertical loads from roof on to the center of wall.
  • Boundary condition 8 is used if there are purlins attached to the face of wall and is not embedded into the wall.

  There are two possibilities for eccentricity at the bottom - 9 and 10.

  • Boundary condition 9 is used if there is a rigid foundation or concrete floor under the wall.
  • Boundary condition 10 is used if there is a shallow foundation under the wall.

After you fill in all the needed inputs, you can press the button Calculate to see the result. If you would like to check the results, you can press Report Generate to create the pdf report, the report and the graph will be create in the folder of the element name, which is inside the NSCE Assessment folder of your work folder.

Attention

When using the tool according to the NPR9998+C1+A1:2020, it is possible that you will get a warning when the calculated element period is shorter than the fundamental period of the building. In that case you are not sure if you can switch to formula H5.a in the the new NPR in this case, please consult with your lead engineer.

Figure 136 Warning to switch formulas.

Guidelines for L4-sheet

L4-sheet guideline for NLTH, NLPO, MRS, NLPO-SLAMA and REF objects: Guideline L4-sheet

L4-sheet guideline for SBS objects: Guideline L4-sheet for SBS

Frequent questions

Note

This chapter includes the questions from all the team members, if you have doubts during the NSCE or NLKA assessment, please send your question to taskforces, they will communicate with the knowledge team.

1 - Inclination angle θ

Figure 137 Mechanism wall out-of-plane.

1.1 - The θ used for outer leaf or other NSCE elements – How should these be obtained from the NLPO analysis?

The actual θ can be calculated from the performance point of the NLPO analysis, which is the deformation at the performance point of the perpendicular supporting walls.

For conservative assumption, θ = 0.015 should be used for building with either rigid or flexible floors.

If by using conservative values, UC check is greater than 1, then it is better to use actual value of θ based on results of pushover analysis. To calculate θ from pushover analysis, two things are needed. First, the performance point in each direction and second, the displacement at the top of element under consideration at the performance point step.

For walls (or elements) which are along X-axis, use the performance point for Y+uni, Y-uni, Y+mod, Y-mod. Out of the four performance points in Y-direction, select one which leads to maximum value of inter-storey drift. To calculate θ, use the following expression

\[θ = \frac{interstorey \ drift}{storey \ height}*100\]

An example for calculating θ using this approach is shown below.

Figure 138 Example of a wall.

• Case = Y Negative Modal

• Performance Point = Load Step 348

• Floor displacement (DtY) at Load Step 348 = 24.8 mm

• Wall under consideration = ‘N0-WANDEN-MW-KLEI<1945-210-9’

• Height of wall = 3.74 m

\[θ = \frac{24.8}{3740}*100 = 0.66 %\]

1.2 - The θ used for other NSCE elements – How should these be obtained from the NLTH analysis?

For conservative assumption use θ = 0.015 and only for long barn walls it is suggested to use θ = 0.025.

2 - Chimney

2.1 - What is the limit of the height for the chimney, parapets and gable walls to choose for whether or not generic risk assessment is suitable?

Categorize the element by the table 2.2 in NPR, then assess with the corresponding return period. About the chimney in the below picture, this is an exception, when think of chimney, it is usually not a large element.

Figure 139 Peculiar chimney.

This element may function as a chimney, but structurally it is more complicated. Assessing it as a chimney is not applicable.

2.2 - How should we assess the chimney ducts (shown in the below picture)? Should we assess their out-of-plane capacity?

Figure 140 Chimney duct.

First of all, this element should be identified as PSSE or NSCE. For the chimney ducts it is normally NSCE, then follow the procedure to assess the NSCE element.

Figure 141 Chimney structure and duct.

• Chimney ducts strength is assumed to be sufficient because they are small length closed structures with high stiffness (high support for the perpendicular walls in the out-of-plane demand).

• In case of inclined ducts the situation is different. They either shall be supported by a timber frame or be replaced by lighter weight ones. If the latter is chosen, the chimney on top shall be replaced by a light weight one as well because, if we remove the duct below the chimney requires support. GMC provides measures for supporting and replacing the inclined ducts. However, it is highly recommended to support the inclined ducts with timber frames instead of replacing them as it is, by far, a cheaper solution. In this case the chimney shall not be replaced anymore.

3 - Triangle wall

3.1 - When using semi-probabilistic assessment to assess a triangle wall, how to decide the height and center of gravity? Refer to the below pictures.

The height should be till the highest point. The center of gravity is the mass center of the element.

4 - Frequency

4.1 - The frequencies for NSCE assessment for NLPO and NLTH. Obtained from eigen frequency analysis of the flexbase of entire model? Or somewhere else? Additionally should these be based on the eigenfrequency of the entire model, or of the individual elements (in case of outer leaves for example)?

Here the frequency refers to the fundamental frequency of the building.

• For NLPO: the frequency T ₁ for the assessment can be derived from the bilinearized push-over curve at the performance point. Use 3 Hz as a reference in this case.

  

  Figure 142 Formula to calculate the frequency from the results of NLPO analyses

• For NLTH: if there is no clear dominate eigenmode, use 3 Hz for the assessment.

5 - Overburden load

5.1 - We now obtain the overburden load based on the A1 Static analysis for each individual wall. However, this is based on the assumption that during the earthquake period, there will never be complete loss of compression at the top of the wall, even due to possible overturning. Is this a correct assumption? Sometime we do see loss of connection between the wall and the floor.

The overburden load obtained from static analysis is sufficient.

5.2 - When we have a end wall connected at the floor level, how do we consider the overburden load from the upper gable wall?

Take the following object as the example, the whole mass of the gable wall is resting on the lower part, so you can distribute that whole mass pragmatically but realistically as imposed load on the lower part. For example the pier on the left will carry about 1/3 of the whole gable and the pier on the right 2/3.

Figure 143 Example of gable walls.

6 - Gable wall

6.1 - For the gable wall in the following picture, is it correct to separate the assessment of the gable wall into these two parts? Do we need to assess the part where the outer leaves fall onto the roof? Do we need to assess the part where the outer leaves fall into the area of the exit route?

|gable_wall_2|

First since part of the wall can fall onto the roof then public space, and part can fall to block the exit. The wall needs to be assessed.

• If it is an gable wall, the generic risk assessment is applicable here.

• If semi probabilistic assessment is applied, then with different boundary conditions different parts of the wall can be assessed separately.

6.2 - What is the definition of gable wall?

As is shown in the following picture, only the top triangle part is defined as gable wall. In this case we assume that there is a proper connection of the outer leave to the roof elements. Therefore, the generic assessment for the gable wall can be applied.

Figure 144 The definition for gable wall (in red contour).

7 - Stairs

7.1 - How to assess the stairs? Generic risk assessment by assuming the category of chimneys is applicable? Timber staircases would generally pass on the first category, Mortal danger. However, for heavier staircases this process is still a bit unclear.

• In case of timber stairs, no need to assess. See NPR 4.3.6.1 condition 1.

• In case of masonry or concrete, use the generic risk assessment. This is comparable to gable wall from 1920 (type 4 in table 9.8 from UPR), category 1. From the below graph we can use 0.35 g as the capacity.

Figure 145 Reproduction and extrapolation (dotted) from figure J.1 NPR9998:2018

• For the stair cases, if they are timber or steel, their failure mode would be predominately vertical. In reality we don’t see them failing with gravity. The vertical component of the earthquake loads are very low compared to the horizontal ones. Those stairs are flexible in the horizontal direction, in which case they are considered to be safe.

Warning

This only applies for stairs in good condition. If you see rot timber, cracks, beams bending, etc. Then it is a special case, discuss this with your lead engineer.

Figure 146 Reproduction and extrapolation (dotted) from figure J.1 NPR9998:2018.

8 - Green house (conservatory structure)

8.1 - When is a conservatory structure an NSCE? If it is NSCE, how to assess it? See the pictures below.

|conservatory_structure_2|

• In the left picture, the structure is an separate building:

  First discuss with the lead engineer to see if it is in the scope of your object. Model the building in the model if it is in the scope. If it is an separate building, the consequence class is CC1b, timber structure frame functions as PSSE.
• In the right picture, it is in the main building:

  If it is in the main building, as an opening, no further action needed.

9 - Dormer (dakkapel)

9.1 - When is a dormer an NSCE? If it is NSCE, how to assess it?

Figure 147 Example of a dormer.

• If the material is timber, no need to assess.

• If the material is masonry, consider it as NSCE, comparable to a chimney in the generic risk assessment. The NSCE category is category 2 in the below table from UPR.

• The triangular parts of the dormer, on the sides are very stiff, which does not cause a problem. In this case, the load is considered to be taken by the roof, so the dormer is deemed to be safe. On the other hand, the roof has a opening in the place of dormer, which degrades the diaphragm behaviour. The loads from the dormer act on the edges of the dormer, aka. the opening edges.

• By experience dormers of size up until 3 m x 3 m are deemed to satisfy.

10 - Wall not in the spanning direction

10.1 - How do we characterize a wall that at the end meets the roof plate, with the roof plate spanning in the other direction, i.e. not supported by this wall. A cantilever or do we assume some connection between wall and roof, i.e. et = -teff/2 and q=2.

It is not cantilevered, the wall is supported at the top.

The top support used for the assessment is depending on the support conditions.

For the angle we can use 0.025, overburden load on the wall is 0.

11 - Walls of aerated concrete blocks (gasbeton)

11.1 - How do we assess the walls made of aerated concrete blocks as are shown in the following picture?

Figure 148 Aerated concrete walls.

Walls of this material are masonry (glued) and it seems weaker than calcium silicate blocks in table F.2 of NPR9998:2018+C1+A1:2020. Therefore, please apply NLKA for those aerated concrete walls as permitted per section 4.3.6.3 of NPR9998:2018+C1+A1:2020.

• If the walls of gasbeton (aerated concrete) have a thickness of less than 75 mm, there is no need to check them.

• In the UPR says aerated concrete density is: 800 kg/m3

• So it should be used the NLKA tool and considered the density of aerated concrete in the UPR

12 - Walls made up of timber

12.1 - How do we assess light-weight walls made up of timber columns with plywood or timber sheathing on both sides.

Figure 149 Timber wall frame with an opening.

In NPR9998:2018+C1+A1:2020 section 4.3.6.1. it is stated that no assessment is required for vertical NSCE elements that are smaller than 3m and lighter than 60kg/m ² because it does not pose potential lethal hazard. The self-weight of the timber frame wall is about 20kg/m ² based on the typical dimensions that are given below. Therefore, no assessment is required for timber frame walls that are smaller than 3m. If this requirement is not met, the timber frame wall should be assessed as indicated below.

To check such a wall, L4 spreadsheet may be used. Go to ‘Wand vervangen_SK’ sheet. This sheet is used to check stability of masonry walls retrofitted with timber frames. But this sheet may also be used to check timber frame walls as NSCE once all parameters linked to masonry walls are set to zero, so that only the timber frame capacity is included in calculation. See picture below.

Figure 150 How to fill L4 sheet for timber walls.

After all masonry wall parameters are set to zero, enter the parameters for timber wall. In the picture below, parameters are set for a timber frame with C18 grade timber, 9mm thick multiplex board on both sides, columns (b x h1, where ‘b’ refers to width of the timber column and ‘h1’ refers to depth of the timber column) of (65 mm x 200 mm) with center to center distance of 400 mm.

Figure 151 Timber wall dimensions.

The unity check can then be read at the bottom of the page. For typical dimensions of timber frame, unity check will be close to zero. Add decimals in the unity check value before adding it in the report.

Figure 152 Unity check.

12.2 - replace:: Timber walls – Knowledge team study

There was a sensibility study performed by the knowledge team showing that the timber walls don’t fail for heights of more than 20m. So there is no need to access them. For a time period T2:

For a time period T5:

Figure 153 Timber wall study for T5 period.

• The moment resistance (Mrd) for a particular section is calculated.

• The mass of the timber wall (m) is calculated and an additional mass of 20kg/m2 of gypsum plates are assumed that covers the timber wall.

• Regarding the calculation for the acceleration, further points are considered.

  • Minimum Tb value from the Groningen province.

  • Maximum Peak Ground Acceleration from the Groningen province (rho).

  • Maximum Amplification factor from the Groningen province (PGA).

  • Maximum Tc value from the Groningen province.

• This gives a wide range of constant seismic demand, as shown in the image below. Important to note that the maximum and minimum values for the acceleration parameters are not for a particular location but from the entire Groningen province.

Figure 154 Graph X-Y.

• Using the above method, the seismic demand (Acceleration) is calculated. Finally, the following formula is used to calculate the Maximum Height of the timber wall (h).

  𝑀_𝑅𝑑=(4∗𝑚∗ℎ^2∗𝐴𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛)/𝜋^3

• In such a way, the maximum height for the timber wall can be calculated.

• These points can be added to the starting point documents (UPR) for the NLTH and MRS, so that a generalized conclusion is obtained.

13 - Walls made up of steel studs

The sheet for checking such walls is under development. This section will be updated once the sheet is developed, checked and approved by knowledge team.

14 - Horizontal platforms

14.1 - How do we assess horizontal platforms

• The cantilever shows that it has enough support connection to handle loads from wind and snow, which should be covered already in the static situation.

• These elements are not considered as NSCEs. Discuss with your lead engineer to see if these elements should be in the model.

Figure 155 Horizontal platform example.

Figure 156 Horizontal platforms structural scheme.

15 - Glass brick walls

15.1 - How do we assess glass brick walls

• A study developed by Joep Sluijs with the supervision of Peter Flink was made for this kind of walls.

• In this section is presented the steps of how to asses glass brick walls

• The next picture show’s the building with the wall under study:

Figure 157 Horizontal platforms structural scheme.

Glass brick wall

• Height = 7.6 m

• Thickness = 0.08 m

• Density = 900 kg/m³

• NSCE category 4 → return period 2475 years

• Assumptions:

• Cantilevered

• Initially use NLKA tool

Figure 158 Use the NLKA tool to check the glass wall.

• The use the L4 sheet to check the wall.

Figure 159 Use the L4 sheet to check the glass wall.

Alternatively is possible to assess this wall with a wind load prespective

• Alternative approach to assess the NSCE wall

• Can be used to assess when traditional methods all conclude failure

• Based on NEN-EN 1991-1-4+A1+C2+NB

• Province of Groningen falls under area II

• Idea is that wall should be designed for a certain wind load/pressure

• The pressure is determined with:

Figure 160 Equation for obtain the wind pressure.

Figure 161 Equation for obtain the wind pressure.

Figure 162 Extreme wind pressure.

Figure 163 Pressure coefficient C_pe .

Assessment results

• Wind pressure:

w_e =𝑞_p (7.6)∗𝑐_pe =0.58∗0.8∗1000=464 𝑁/𝑚²

Seismic load on wall: 𝑝_seismic =𝑎_g,d ∗𝑝∗𝑔∗𝑡∗𝜌_glass =0.11∗2.375∗9.81∗0.08∗900=184.5 𝑁/𝑚²

Unity check: 𝑈𝐶=𝑝_seismic /𝑤𝑝_e =0.40

Wall complies according to wind load assessment